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What do you guys do when you are milling a tight tolerance hole with an endmill and can feel a taper towards the bottom. Assume it's a new endmill that's interpolating (ramping down) down the hole. I've heard everything from speed up rpm, to slow down rpm to slow the feed down.
On a cnc machine, using gauge pins to check the hole.
Second finish pass?
Use a boring head set to size for the final pass.
Ian.
hi john :) rough until depth=h using a tool with normal chamfer, then finish until depth=h-0.03eq using a tool with smaller chamfer; for this to work, you need to measure both tools at same moment, because tool measuring senzor results values changes during a day, mostly because of termics
depending on setup, you may consider prefinishing with another tool, so to be sure that the finish tool is always cutting in constant ae; like this, using a 3 tools combo, you may push the roughing tool for longer
kindly :)
Using gauge pin to check the hole????…..did you know that a 20.00 mm diam pin.....whatever...... is a press fit in a 20.00 mm hole?
I assume the gauge pin is not a regular plug gauge with "go" and "no go" end sizes.
Ian.
hello handlewanker :)
reading this, i remembered the dimensions translations, caused by the measuring method : for example, if a part has to be delivered with a bore dia20+0.03, then the actual size of the "good" part will be different, depending if it is measured with :Quote:
did you know that a 20.00 mm diam pin.....whatever...... is a press fit in a 20.00 mm hole?
... an into or cmm ( this measuring method may deliver the smallest bore )
... an internal micrometer
... gauges ( this measuring method may deliver the biggest bore )
in other words, if inside a shop is aplied a measuring method which is different then the method which is apllied at the client, there is a big chance that the client will reject "good parts", or accept "bad parts"
this dimension shift problem is very accentuated when tolerances get smaller, and measuring method is not discused
each measuring method, in order to validate a part as being "good", requires a different range for the bore tolerance and cilindricity :)
a few years ago, i was in the situation to explain why 15um got shifted; lucky for me, the client understood, and the discussion was short, otherwise it could end in a messy situation :)
you mean those sets, for example, if you have to deliver 20+0.03, then is ok to have gauges 19.95 19.96 19.97 19.98 19.99 20.00 20.01 20.02 20.03 20.04 20.05 ? each one ±3um kindly :)Quote:
I assume the gauge pin is not a regular plug gauge with "go" and "no go" end sizes
No....you need to have a plug gauge that has been made and calibrated by a company that makes gauges to be such a size that it will indicate the hole size required by the go and no go method......the customer MUST also use the same plug gauge to check the hole and it will be the same size as the one you are using.....there are no ifs and buts for that.
You can gauge a hole with a telescopic gauge or an inside micrometer etc and it is the fit of those gauges and the skill of the person using them that determines the hole size.
It can be said that no two people can measure a part with a micrometer and get the same results mainly due to one or the other using more or less pressure when applying the micrometer….whatever.
A go and no go plug gauge MUST enter the bore with the go side and MUST NOT enter the bore with the no go side.....that is the only way to give a customer the results that his drawing tolerance states.
It is also a fact that the plug gauge is made specifically for the size indicated by the customer's drawing tolerance.
You cannot just stick a gauge pin in a hole and think it's OK......gauge pins are also made to a tolerance which is a one size only.
You cannot make a plug gauge to check your work for a customer unless you have accreditation as a gauge maker.
The fact that plug gauges are expensive and must be made to measure means many people forgo their use and rely on measuring their work piece with conventional measuring equipment.
With batch work the cost of a plug gauge is ALWAYS costed to the customer and it is your guarantee of integrity.
For example, where would you get a plug gauge to measure a 20mm bore that had a tolerance of plus .02mm and minus .04 mm.....those sizes are pretty slack and you could easily supply a part by measuring with an inside mike or a telescopic gauge alone......if your parts are on top limit they may be over size if you measure wrong......a plug gauge does not lie.
If you are making many parts to a drawing then a plug gauge is a must have item.
Ian.
hi handlewanker, nice infos there / in some cases, i craft gauges, or even simple measuring fixtures
however, so far, i had encountered setups that required extra-length of the go-gauge : in some situations, i have used go gauges 3d - 10d, and even combined go-gauges, like one that is 6d+6d, designed to check if 2 holes are cilindrical and coaxial
there are parts that a cmm can not even touch, or, even if it does, it requires too much time to run the inspection, and results are questionable; i am not saying that a cmm is not ok, but in most situations, i preffer to have the measuring instruments near the machine ... this requires a few things, like clean hands, clean machine cabinet, no temperatue fluctuation, etc
to eliminate doubts, a go nogo gauge, depending on dimensions, should have some friends :Quote:
the customer MUST also use the same plug gauge to check the hole and it will be the same size as the one you are using.....there are no ifs and buts for that
... go nogo, for the go side ( go go, and nogo go )
... go nogo, for the nogo side ( go nogo, and nogo nogo )
... and, of course, these :
...... go go go + nogo go go , go nogo go + nogo nogo go
...... go go nogo + nogo go nogo , go nogo nogo + nogo nogo nogo
is not common to use so many gauges, unless there is mass-production
... "main gauge" is crafted within tolerance T
... "calibration gauges", to verify the "main gauge", are T/3
... "factory gauges", to verify the "calibration gauge", are T/4 .. T/5, depends
and, there is the frequency of usage :
... "main gauge" : every part, every 10parts, or daily
... "calibration gauges" : once at 4 hours, daily, weekly
... "factory gauges" : weekly, montly, yearly
and there are the documents :
... "main gauge" results are not recorded, or maybe is used an "inspection template"
... "calibration gauge" results are not recorded, or maybe is used an "passport"
... "factory gauge" results are always written insisde the "passport"
and the real location :
... main gauge - i preffer as near the machine as possible
... calibration & factory - a bit far away, in a less hazard place, like a peripheral room, under the sink, etc
in other words :
... in most cases, is enough to buy a go nogo gauge + calibration certificate
... for long term setups, is ok to buy/have also the "calibration, and maybe the factory gauge" + passport
is not a must to buy the "calibration/factory gauges", as long as there is a method implemented in order to check the dimensions of the "normal gauge"; but, if this method does not exist, and someone forces a gauge, thus uses too much force on it ( or gauge life is near end ), then :
... acceptable tolerance field gets reduced ( this is the nice case, as long as the process is still stable within the new-reduced tolerance )
... tolerance gets shifted, or even out of initial specs ( at this point, derogation documents kick in, tring to save as many parts as possible; if a part is out of the derogation, is trashed; derogation, depending, may allow the tolerances to shift with 5-20% )
again, depends ... kindly :)
No matter what you are using, a new gauge or a well used one, as long as the calibration certificate is current then the part is what the gauge says it is.....that is beyond question...….if your customer's gauges are not currently calibrated they have no valid reason to fail or reject your production...…..a current calibration certificate is holy writ.
Ian.
yup ... on some setups, is easier when the client gives you the crafting steps + control; something like : "here, take this, just replicate" - i love those ones :)
about certificates, papers, etc ... some persons always check a gauge the 1st time they put their hand on it, regardless of that gauge being new or old; is a minihabit, like checking the caliper, micrometer, etc / kindly :)
Well, I can't agree with you on that......a gauge is a set piece and it only checks the dimension that it is made for during the calibrated period of time.
Gauges are calibrated periodically by a gauge maker who is accredited to do such work.....an ordinary person at the machine CANNOT check a gauge...…..and for that matter a micrometer or a vernier caliper or even a digital caliper.
Plug gauges CANNOT and SHOULD NOT be checked against a set of slip gauges as the slip gauges need to be calibrated too.
Did you know that a micrometer normally comes with a setting piece, but that only checks the maximum size range of that micrometer size and cannot check it's screw thread from zero to the big size end......they do wear and must be calibrated periodically etc etc
BTW....if a customer doesn't give you specific sizes to make a part for with the tolerances clearly marked you may as well use a tape measure.....LOL.
Ian.
"plug gauges" are checked with "caliber gauges"Quote:
Plug gauges CANNOT and SHOULD NOT be checked against a set of slip gauges as the slip gauges need to be calibrated too.
"caliber gauges" are checked with "factory gauges"
not everybody, but few can ...Quote:
an ordinary person at the machine CANNOT check a gauge
most operators have normal gauges
few of them, the shift master and the control room has acces to calibration gauges
control room has also factory gauges
and also, there are other things, in other points; is not everything in one place, at one person; kind of a cross-reference
maybe there are ( 10+ 20+ ... 50+ ) plug gauges, and 5 calibration + factory gauges
maybe few persons are empoyed only for managing gauges & passports
that is reverse enginering :) just saying / kindly :)Quote:
BTW....if a customer doesn't give you specific sizes to make a part for with the tolerances clearly marked you may as well use a tape measure.....LOL
I still disagree with you...…....end of topic.
Ian.
look handlewanker, you are right, is not ok to check with another gauge, is not common behaviour
also, future perspective, is hard, when it comes to find good workers
there are still places with a high level of experimented people; some places still have 1:1departments, other are 1:3 or 1:5; such things are pretty high, but i don't know for long
average is below 1:10, or 1:30, and this is an average from 30 yrs ago
what i had been talking about is not common, since shops tend to be sporadic, but there are still places that are centralized
ok, let's say that you have hundreds of gauges at hundreds of people ... how do you check them ?
Who cares!! The OP never even mentioned the tolerance of the bore he is working on. He only said that he is using gauge pins to check the hole and could tell the interpolated bore was tapered. A gauge pin may be just fine depending on the tolerance requirements. He simply asked how to take care of the taper.
This time I disagree with most posts.
We did not get original posters d/l tolerances .. which are what it is all about.
And size, depth, speed, qty goals.
A reamer will deliver a hole about 0.01 mm in size, or a bit better, and mostly follow the bore while improving it a bit in straightness.
Carbide reamers will make the hole straighter, and double-reaming will make the hole straighter and more uniform.
Typical holes made with boring heads or modern vmc machines will have 0.01-0.02 mm tir/taper, to 0.04 mm (weak) bore sizes and straightnesses in the normal 1-3-4 d/l ratios.
LOL....a veritable storm in a tea cup...…...the problem I highlighted arose form the ongoing conversation/post.....whatever...…..and concerned the aspect of a customer supplier relationship when it comes to producing work to a customer's toleranced drawing., so I suppose it doesn't matter if the hole is not to the tolerance as long as it's parallel.
As long as the gauge pin, no matter what size it is, goes into the hole it will as you say tell you if the hole is tight at the bottom…….I can't imagine what you would make of it if the hole was tight at the top and oversize at the bottom.
Ian.
hello, yup, i started it :) i just remembered that a while ago, there was a calibration loss near the limit tolerance ... whatever, like you said, agreing with the client on control method helps :)Quote:
LOL....a veritable storm in a tea cup...…
i don't understand this :)Quote:
so I suppose it doesn't matter if the hole is not to the tolerance as long as it's parallel
sometimes this happens ... for example part is controlled inside the machine and is ok, but after it is taken out, sometimes it happens to be oversized at the bottomQuote:
I can't imagine what you would make of it if the hole was tight at the top and oversize at the bottom
most common cause, is that the fixture puts too much pressure on the part, & the part changes shape
a quick way to check it, is to leave the gauge inside the part, and take the part out : if the gauge does not slip as easy/hard as when the part was inside, or, if the gauge is blocked, than few adjustemnts are made
this is "fluaj", i don't know the english word, rigid material that leaks slowly; unpleasant situation is when this phenomen has effect spread across a time period greater than fewhours-1-2 days
to fix this, it may be enough to program a taper, or to reduce fixture forces, stabilize internal part tension through prior heat-treatments, etc / kindly :)
Lol jesus you guys went off into the weeds. Ok all I'm asking is that say you're milling a .125" hole, or maybe some weird size where you can't just run a reamer through the hole so you have to bore it out with an endmill, or its too small for boring head. And you have a close tolerance to hit, whatever say it's a press fit and it needs to be +- .0002". If, when checking with a gauge pin from a set with .0001 increments, a .1248 only goes maybe halfway into the hole depth its milling to, indicating a taper in said hole, and when you comp the tool on the cnc machine still get an equivalent taper, what are some good tricks to mill straighter holes.
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JS......I think you missed the part where I said......You cannot enter a 20mm diam hole with a 20mm diam pin.....that is a press fit or as we commonly say a size for size press fit.
Go back and read the thread and see where the go-no go gauge application applies.
LOL....and you want to "bore" a .125" diam hole with an end mill....by helical interpolation....LOL...... to a +- .0002" tolerance????….you will get an odd ball size for sure.
Your eventual question regarding "good tricks" to make good holes...…...there are no good tricks...….you need skill and experience to make good holes......good machinery also helps.
A hole that is not a standard size and is relatively small in diam would have to be bored with a boring head or a specially ground undersize reamer....or perhaps an adjustable reamer, but hitting the +- .0002" tolerance would be very tricky to say the least.
BTW.....if the job volume is not sufficient to cover the cost involved in getting a hole to such a tight limit....give it away and move onto more profitable work.....you have to know when to fold them, know when to hold them and know when to walk away etc etc.
Ian.
hy john, there are a few tips spread across a few posts, but i also started a bit of off-topic conversation, making it hard for you to spot what you needed, so here it is :Quote:
Originally Posted by JOHNSMITTY
... all ok until post 5 inclusive
... post 16 is ok
other tips :
... lower feeds, because higher feeds will mess the cilindricity
... low overhang
... "through hole + vertical reamer" is better than " blind hole + horizontal reamer "
... a toolholder with tir adjustment
... using a shorter go gauge, because longer ones require improved cilindricity
* in the end, is all about tolerances
this is all i can think of now / kindly :)
Just as Ian said, use a boring head to ensure cylindricity. If is a single part or a small batch I´d rather use a holtest micrometer to measure the bore.
Greeting
Ari
Quote:
Originally Posted by handlewanker
hello, about reaming / cilindricity, etc, this is a pretty common thing; truth is that is much easier and reliable only to drill, while reaming may take longer
is ok to rough, is ok to finish, but is less productive to debur or ream ... so there are operations that are more productive than others, and a cnc which runs non-productive operations is less-profitable; this does not mean that it is not profitable :)
from this consideration, some shops avoid reaming operations on the cnc's; simply, because it is not productive, at least on small batches
so, is about some shades of gray / how do you believe that is organised such a shop that does not ream on the cnc ? kindly :)
A reamer is an all time standard tool to produce holes quickly to size time and again...…..if you resort to just boring a hole with a boring head it will take longer even if it is a superior straight round and to size hole...…...in production time is money and a reamer will save time every time.
That would be my first go to tool for a hole solution...…...alternatives go down the more time and less accuracy ladder.
You can take a standard to size reamer and regrind it to suit your drawing tolerance if the drawing requires a non standard size etc......for low volume work, say 3 or four parts then an adjustable reamer or a boring head will do the trick as they're infinitely adjustable.
I cannot imagine why a CNC situation requires a different approach.
BTW....before I retired, when I was still employed as a production planner, I tooled the CNC's with carbide tipped reamers every time......this was back in 1990 - 2000 era....have things changed since then?
It may be quicker to just drill a hole but a drill won't cut to a tight tolerance size, give a good finish or be on position.
Reaming after drilling also is not an answer as the reamer will just follow the drilled hole and that can be out of position...…….the proper sequence must be followed if you want to get work that passes inspection both for size, finish and positioning......but pigs can fly too under certain conditions.
Deburring can be done with a vibro finishing machine or a tumbler.
Ian.
oau, i forgot this thread :)
all these are frequent aspects :Quote:
in production time is money and a reamer will save time every time
... tool costs, especially non-standard sizes
... tool delivery time
... setup time ( alignment, tir check, etc )
... adjusting cutting specs
... holes that are too big /too small, even if the reamer dimension is ok
... almost no chips at all, on a machine that is capable of delivering chips
what about improving all these aspects ?
please, what alternatives exist, and why are those with less accuracy ?Quote:
That would be my first go to tool for a hole solution...…...alternatives go down the more time and less accuracy ladder.
the reamer is not always following the hole; each setup is a balance between elastic & plastic deformationQuote:
Reaming after drilling also is not an answer as the reamer will just follow the drilled hole and that can be out of position
for a reamer to follow the hole, then the elastic component has to be dominant, alowing the tool to 'move' inside the hole, and shift back to it's original position, when it is out of the hole
for a reamer to not follow the hole, the plastic component has to be dominant; this can be achieved, for example, with a rigid spindle + short overhang tool with long flutes
each machine, in time, increases it's elastic behavior, thus is losing rigidity; for a process that delivers tight tolerances, then this effect has to be postponed as long as possible
what can be done ? analyze the frequency of the holes, and dimensions
... get a set of after-drilling tools ( they look like a reamer, but with less flutes, and they are more rigid then a drill; the trick behind such tools is that they don't copy the hole, and can straigthen-up a tilted hole, delivered by a long drill )
... get an attachement ( eccentric boring or grinding attachment, honning attachements )
... put that attachement on a ' normal ' machine, and leave it there : voila, this is a low-cost specialized machine, that never runs roughing operations, spindle is not under frequent tool changes, etc; like this, the machine keeps it's accuracy for a looooong time
... get a specialized machine
i don't say that a reamer is bad; i say that controlling costs and analyzing downtime requires patience and time, and seeing such alternatives in action may help / kindly :)
If you aren't into reamers for hole sizing then you have missed the plot completely......even odd size holes will profit from a reground reamer if the volume is great enough.
As I said, a reamer will ALWAYS follow a drilled hole without exception......because it has flexibility in it's length.
If you apply the length to 4 times the diam rule you get a boring bar.
Reamers also cut on their ends not on their sides.
Reamers cannot make a hole true to a required position if the hole is off centre......then the reamer will be off centre too.
There is an alternative way to make a hole to size and positioned accurately too but it is not profitable.....it's called EDM.
When you approach the prospect of a design requirement then you must choose the best way to get an outcome.
BTW....you "could" produce a hole to size and position with an end mill, but the flutes would need to be blunted to prevent them from enlarging the hole diam and in so doing making the endmill a short series reamer.
You "can" make a drill cut to size by predrilling the hole with a drill 10% undersize and stoning a slight radius on the corner of the end flutes of the finish drill.
Ian.
hi, i discuss methods to deliver straighter bores; this also includes reamers :)Quote:
If you aren't into reamers for hole sizing then you have missed the plot completely
with all respect, this is not true ...Quote:
a reamer will ALWAYS follow a drilled hole without exception
when the reamer follows the hole, it is because of a few factors; this includes the length/dia ratio of the tool, but is not the only one; another aspect is the console&chucking flexibilityQuote:
because it has flexibility in it's length
for example :
... classical lathe : you expand the tailstock, or even push the entire tailstock by hand
... classical mill : you lower the head
* in above situations, the console is flexibile
on a cnc, consoles are much more rigid, so:
... if you wish to to achieve flexibility inside the chucking, you may use floating-chucks, or long-collet-chucks, etc
... if you don't wish for flexibility inside the chucking, then a rigid chuck with short tool overhang is required, preferably with tir adjustemnt ( for mills ), or radial & tilting adjustment ( for lathes )
depending on all these factors, a reamer, during cutting, is somewhere between "reaming" and "boring"
3d : normal quality steel, no internal coolantQuote:
If you apply the length to 4 times the diam rule you get a boring bar
5d : higher quality, internal coolant
7d : carbide, internal coolant
deeper : vibration-dampening
and there are special ones, with section<>circle
by design, a reamer for cilindrical holes has to cut, preponderantly, on front end; if it would cut on both ends, it will recut the hole when it is retracted; or, even worse, it may get stuck inside the holeQuote:
Reamers also cut on their ends not on their sides
a reamer for cilindrical holes should not have cilindrical od, but conical; depending on applications, the conicity of such a reamer can be with bigger diameter towards the front, or with bigger diameter towards the tail ( greater life-spam, etc )
use a rigid console, rigid chucking, and low overhang rigid tool, so to corect the hole position before finishing, with a normal/rigid reamer, or a grinding attachement, etcQuote:
Reamers cannot make a hole true to a required position if the hole is off centre......then the reamer will be off centre too
edm can deliver such things, but it was not designed for such tasksQuote:
There is an alternative way to make a hole to size and positioned accurately too but it is not profitable.....it's called EDM
when it comes to accuracy tolerated holes ( dimension, position, etc ), one may use a coordinate grinding machine:
... the classical hauser
... classical mill with eccentric attachemnt
... interpolating on cnc, with a simple air driven attachement, etc
just saying : a while ago, it was needed to deliver many parts with non-standard holes; i crafted the reamers, i crafted the plungers before the reamers, intenal coolant, tilted flutes, 2 diameters / same tool, etc; all you need is an y-lathe and a grinding machine :)Quote:
When you approach the prospect of a design requirement then you must choose the best way to get an outcome
many believe that a reamer crafted in H7 will deliver a H7 hole, and in reality a lot depends on real scenario, material hardness, fixture tension, etc : all these will affect the life spam and the consistency of the output dimensions; i talk about long setups
instead of blunting the flutes, you may grind the od a bit conical; it's faster :) kindly :)Quote:
BTW....you "could" produce a hole to size and position with an end mill, but the flutes would need to be blunted to prevent them from enlarging the hole diam and in so doing making the endmill a short series reamer
Lots of excellent posts and comments on hole size, reamers, production, straightness, cylindricity.
Basically only holes bored on lathes or bored via boring heads or boring tools on mills are "straight" and "true".
The size of the hole via modern boring head on a lathe or mill, today, is approx 1 micron incremental size.
So holes with 1 micron incremental sizes are easily made in steels if modern boring heads can be used.
Likewise, if the hole has a "good" near-net bore, any reamer will finish it to size, usually with great surface finish.
If better hole sizing is required, after reaming a "good" bore, roller burnishing or ball sizing can make better finishes and smaller incremental sizes.
It is perfectly possible to make ball-burnishing tools.
Sub-micron incremental sizes are reportedly easy to do.
In auto production, VMC cnc mills rough bore the piston holes.
The hole is finished with a single rigid hone coated by diamond abrasives.
Take about 20 secs or less.
The hone lasts 300.000 parts, full year.
Accuracy is better than 0.01 mm in size and tir.
As the actress said to the Bishop, there are many ways to do it.....reaming with a rigid tool is just one way, and the required quality of the end product dictates how you get there.....also, and more pertinent, the volume of the order is the most deciding factor for hole production, and the tolerance just decides the cost.
Ian.
hi hanermo, yup, and also those delivered by coordinate grinding machines, especially because they grind, thus cutting force is low, and remanent tension, inside the part, is really low : this helps to deliver consistent dimensions in soft materials, that, otherwise, because of heavy cutting, may deform in time, at least at micron level; there are cases when parts are ok right after machining, but after a few days, if they are checked again, they are out of tolerances :)Quote:
Basically only holes bored on lathes or bored via boring heads or boring tools on mills are "straight" and "true".
there are cases when the client is not accepting a process that is finishing a part with high cutting forces; so far, this had no been discused in this thread, but, whatever :)
about this "straight & true", i needed to deliver some parts with non-standard tolerated holes, with length between 6-9D, that were checked with a go-gauge as long as the hole; it was a bit tricky, because :
... at that length, all drills would bend, so, after drilling, the hole was not cilindrical, and this was breaking the reamers like crazy; i managed it but using plungers ( some custom tools that would improve cilindricity after driling ), and reamers inside floating chucks; also, i had shorten the active length of the reamer ( thus shorter flutes, but overall tool length remained the same ), to make it a bit more flexible
... also, each part had at least 2 such holes, with tolerated reciprocal positioning : imagine a few H7 holes, that are not paralel, required to be at H7 coordinates, something like a " tolerated swiss cheese "; it was a bit hard, because, if the hole diameter was near the minimal value, then there was a chance to miss the reciprocal positioning; to manage this, i had delivered all the holes near the maximal diameter, i had crafted my own go-gauges ( with bigger diameter then the original ), and i was working in a tolerance that was much smaller then the original tolerance of the technical drawing; in the end, it worked, but it took me a while to figure it out :)
i don't have experience with such tools; i know that they can deliver smooth surface and increase the cilindricity specs, but i don't know what tolerances they can deliver, and, for the adjustable ones, i don't know what is the finess/accuracy of the adjusting systemQuote:
It is perfectly possible to make ball-burnishing tools.
Sub-micron incremental sizes are reportedly easy to do
i believe that they should somehow have a radial play, so to be able to copy the hole ...
i have seen that there are some burnishing tools that may turn, and other types doing some things; i shared the videos at the end of this post
in automotive, it won't be long until they will finish all the engine with a single tool, just like a snake, going from one hole to the other :)Quote:
The hole is finished with a single rigid hone coated by diamond abrasives.
Take about 20 secs or less.
i have seen a documentary about engines, and it said that, if you wish to increase the power, you have to craft the engine with less play between the pistons and the holes, so to lose less power during combustion; when tolerances are tight, it is recomended to heat-up the engine before starting it, because, otherwise, if it would start cold, the pistons may damage the engine; motorsport / kindly :)
https://www.youtube.com/watch?v=eAwqtMtzNYs
https://cogsdill.com/videos/burnishing-tools/
https://www.youtube.com/watch?v=B6YxFxMCKkQ