[joeavaerage]

Hi,
I checked and your spelling is correct. I was very impressed with the design and construction of the Blokart, so very simple but with some very well thouight out design features
that make it fun and safe. I've seen youngsters of ten years get in one and within half an hour are careering around, often getting better speeds than you....damn their eyes!!

This is an excellent example of the sort of design finesse that Mom was questioning. The Blokart has a flexible mast which makes it forgiving in gusty conditions but also
touches the ground first in a 'capsize' which markedly reduces the buffeting to the sailor. The wide spacing of the rear wheels also aids in that the sailor, even in the event of a 'capsize' never hits the
ground. What may not be apparent from a glance is the quite extremme caster applied to the front wheel, gives great turning effect yet does not 'dig in' and flip the kart and sailor over.
All-in-all a very simple and well balanced design. Bet that did not happen overnight!

If anyone reading has a chance to try one....take it with both hands, it will be an experience you never forget.

Attached are a couple of pics of the pattern for my headstock.

Craig

[peteeng]

Hi Craig - being devils advocate - That's a thick short part which would be easy to make out of plate steel. Steel will be twice as stiff as CI. Being thick and short with the open end flanges being restrained as its a bolt flange it won't vibrate so... why go to the expense of castling? Other than "I like CI" and I know your $$$ are limited.. Peter

edit - what is your shrinkage allowance?

[joeavaerage]

Hi peteeng,
the thickness of the cast iron shell is 18mm. the cost is about $900+GST . FEA analysis suggests a stiffness of around 400N/um, which is right in the ballpark of what I want

To achieve the same stiffness would require about 12mm steel plate, and it too results in a stiffness of 400N/um assuming you can get full penetration welds. It would need to be stress relived. The cost of the laser cut steel,
having the welding done (as my own plant would not do 12mm at all well), and the stress relief, and that being done in Auckland amounts to $500-$600NZD +GST.

Lets say I have option 1) at $600 and option 2) at $900, with both being adequate in terms of stiffness, then for the choice is made on the basis of modest cost difference, asthetics and any perceived advantage one has over the other.
I believe the damping that grey iron offers, on the proviso that it be stiff enough for the task, is just too appealing to pass up. Sure, budget is always a concern......but the long term result is more important still.

what is your shrinkage allowance?

Grey cast iron has a shrink of about 1.05% to 1.1% while SG iron has a shrinkage of about 1.6% to 2.3% and plain carbon steel about 2%.

Given that this part will be machined to size shrink allowance is moot.

Craig

[ss6688]

Hi guys
hope your having a good day

I would like to ask if anyone has any suggestion about how to put a price on CNC mACHINING for a client ? by hour , by project ......?
https://cncmillservice.com/custom-ma...machine-parts/

hope you can help me with that

thank you in advance

[peteeng]

Hi ss - You price your services so you make a profit. Peter

Hi Craig - In my modelling of structures like you have designed a lot of the deflection is in the bolting flange. Either make it very thick (the flange that is) or add webs beside the bolt holes. Peter

[joeavaerage]

Hi peteeng,

In my modelling of structures like you have designed a lot of the deflection is in the bolting flange.

I have encountered the same thing. The flange only need deflect 0.1um at the base but result in a 1um deflection at the top. I have experimented with different thickness flanges,
and not surprisingly the stiffness is best when the flange is 300mm thick!!!!...the height of the part. I settled for a flange of the same as the wall thickness, but have a ring of screws to retain
it to the Z axis saddle. The Z axis saddle is itself a 20mm piece (suitably ground) of med tensile steel. It occurs to me that I can make the flange as thick and therefore as stiff as I require
but I cannot do anything about the underlying Z axis saddle, short of swapping it out.....where do you stop?

I can very easily add some thickness to the flange, the pattern is after all MDF, so its easy to glue extra bits on as needed. I may review my FEA results. To date I have been using
20mm diameter raised (only 0.1mm) sections in the vicinity of each screw and then fixing them to model a screw bolted to an infinitely stiff plane. This is my attempt to model a bolted connection.
I have read some of your posts about your modelling of bolts in Fusion. I get the general idea but I don't (yet) understand the details.

Would you be kind enough to post maybe a screen shot of a single bolt model that I might be able to deduce the 'how' details?

I am confident that the part I'm planning to have cast is at least ten times stiffer than the headstock I'm using currently, and that will be good enough without 'going off the deep end'.
Were I to design and build a part that were 'over the top' stiff, all that does is show up the deficiencies elsewhere. Is there any point in over building one part? My existing headstock is the
'wobblyist' bit of the load path....and I seek to correct that, but am not trying to make a 150N/um machine out of a structure that will be 50N/um at best.

Craig

[peteeng]

Morning all including Craig - As you say everything is connected so where do you start/stop? Its best to sort this in the design rounds so the total picture can be made consistent and commensurate (commensurate is the word of the day) I suppose you make the column solid In regard to bolts I'm getting my head around how F360 deals with analytical bolts. Its running a job at the moment so in summary; In simulation you can place an analytical bolt using a bolt constraint. You select the hole opening and then this gives you the option of a nut or a blind hole. Pick the option and then select the nut end or hole end. This will create a bolt the same dia as the selected hole (but you can change the dia & material in the table) Then apply a preload if needed. This sorts the bolt. Unfortunately at the moment you have to do this on a hole by hole basis. Would be great to be able to select more than one hole at a time. Now the faying surfaces your holding together need to be changed from a bonded connection to a separating connection. This is done in the contacts manager. Select one part (right click) then (select related contacts) and change the bonded connection to separating and include a friction co-efficient. (dry steel 0.35 dry aluminium 0.6 look up a suitable co-eff) Now you have a preloaded bolt, a friction connection and your done. The default mesh size needs to be improved so go to mesh controls and make that a bit finer. I'll do some screen shots latter. This morning I have been running parallel f360 and simsolid models comparing results.

In above I assume you use auto connections up front so all faying surfaces get bonded. Then work through the contact list and set each contact to the desired contact type. There are symmetric and asymmetric connections, For machine design use symmetric. Its very unlikely you will come across a unsymmetric contact. This mainly occurs in cases of sliding contact and we don't want any sliding!! ie one side is static the other slides.

Some of the more detailed runs in F360 fell over this morning and take 30mins or more to solve/fail. SS solves in seconds even at high resolutions. But the results so far are that a dowelled and well designed bolted connection is 93% say better then 90% efficient compared to a welded joint. I will also set up and run a welded beam so the weld size can be looked at. This indicates to me that for Maker level builds or a one of build its worthwhile going down the path of a 100% bolted machine in steel or aluminium. Welding is fraught with issues. By bolting you can machine parts to the accuracy you want, adjust the assembly if needed and use dowels if required to gain that little extra insurance. My models are running with Class10.9 bolts preload and the connection got stiffer going from C8.8 preload (14kN) to C10.9 preload (20kN) and I'm running one now at C12.9 preload M8 (25kN). In my assemblies I also use wicking loctite once happy with the fit. Bolted connections are damp due to micro friction. In texts they are as damp as CI and use up to a 2% damping factor which is quite damp for a structure. Once I'm confident in F360 bolt numbers it can be used in confidence... sounds odd but even simsolid has various issues with bolts that need "interpretation" to dodge the issue. Peter

[peteeng]

For those interested in bolt FE. When you bolt a connection together you create something greater than the parts. You create a large stiff spring system. This is a combination of the part compression (due to the preload), the bolt extension and the friction in between. Its a simple exercise to predict how a single bolt behaves using manual calcs. It gets complex when many bolts are used close together, But it seems modern FE can do this pretty easily so we can take advantage of this and design bolted connections vs guessing at how they perform... I think bolted assemblies are the future for Maker level machines vs welded. We seem to be married to the idea of welding machine structures yet are happy to bolt our rails and cars and various bits together.
Aircraft and buildings have been bolted (and rivetted) together and they have stood the test of time and effort for over 100 years... Peter

I've been using steel friction as 0.35 as thats the std value in AS4100 for steel structures. I have been involved in friction testing and have tested higher than that. Here's some numbers from NASA. steel 0.7 and alum 1.0. Most FE systems won't accept values higher than 0.8 for various reasons. I just mucked with fusion and it happily accepted 1.0 in the separating values so that's good. I'm interested in aluminium as I can easily machine Al on my router. Then there's the plus effect of loctiting the surfaces together that's extra adhesion over the friction. I can model this in simsolid but it gets tedious. I think we can bond the surfaces together in FE,in the knowledge its 90% efficient... and set the design rigidity target at 2x the needed.... then fail to get there but that's life.

edit - I ran the beam at 0.7 and its efficiency went from 93% to 97%.. The bolt spacing is 200mm and it has 8 bolts. I could up the bolt count and it will get to 100%. Aircraft people just put a rivet every 2" and do no calcs. So use enough bolts and its 100% I'm happy with 97% so I'll bond and call it quits and use lots of bolts and loctite.... Peter

and this discussion is also relative to the connection strain. In machines the part strains are really small because the parts are really stiff. The test beam has 10Mpa in the parts this is high for a machine part. So the connection strains in a real part will be really small, no where near the slip strains...

[joeavaerage]

Hi peteeng,

I think bolted assemblies are the future for Maker level machines vs welded.

From a pure DIY point of view I tend to agree......but it need not be. I priced thermal stress relief here and it costs $6.70NZD/kg or about $4USD/kg.
If you had 100kg of welded steel parts....then $400 to stress relieve. Sure its not cheap, but its not going to break the bank either. Why is it hobbyists
consider stress relieving as 'verboten'?

Additionally I've come to realise thermal stress relief is far from a complex or demanding task. There are dozens of pottery kilns out there which can all very handily exceed
the 650C required for stress relieving steel.

Hobbyists need to get over their fear....its just not justified.

Craig

[peteeng]

Hi Craig you still have to transport (twice) and finish machine the large parts. If you are going to make parts on a CNC, design them so they self assemble and your done. Plus you can pull it apart and move it. There's quite a few large machines in basements (in this forum and others) that create all sorts of issues for the Maker... Including me, that's why I have a 50kg limit on parts... ... Peter

[joeavaerage]

Hi,
transport costs are going to be incurred no matter what.

If you want to get stable performance from welded structures the you need to stress relieve....its that simple, and while its not cheap its still only a modest cost in a machine build.

In your professional career you specify heat treatments as a matter of course when needed, why should a hobbyist not do the same?

Craig

[peteeng]

Hi Craig - Because many hobbyists can't. They are either a long way from such services or that service does not exist or they live in "hope" that it will work out Ok if they choose another Path. Of course, if your welding and have TSR services available then they should be used but many people don't. So I am proposing another viable way to make a machine with a bit more certainty. I'm sure I could weld your column and have it finish machined in steel with no heat treat and it would work out. Saving the transport to/from the TSR. Also I could make a bolted assembly and it would work out to... But some objects would not work out if you didn't TSR and they will be a source of great frustration and rework... experience and budget drive many of these decisions (or maybe better to call them delusions)... Peter

Hey Momentz - Have you released your Lanko casting yet? Peter

[joeavaerage]

Hi,
the nearest specialist heat treatment facility from me is Auckland, 1500km away and over Cook Strait....so its not close, but its still not impossible.
If making CNC machines were easy everyone would do it.

I think in fact hobbyists shy away from it on cost alone, and perhaps secondarily because they don't actually search out the companies that do it. But as I mentioned earlier
how many pottery kilns are out there....hundreds upon hundreds.....and they would do TSR in a canter. If hobbyists would overcome their initial aversion they just might
find that it is in fact perfectly viable....and that in turn would open up the opportunity to weld your machine together....which is just so cheap and versatile.
So being a bit more realistic about TSR actually brings a hugely valuable method into the mix.

Craig

[Momentz]

Hi Craig - Because many hobbyists can't. They are either a long way from such services or that service does not exist or they live in "hope" that it will work out Ok if they choose another Path. Of course, if your welding and have TSR services available then they should be used but many people don't. So I am proposing another viable way to make a machine with a bit more certainty. I'm sure I could weld your column and have it finish machined in steel with no heat treat and it would work out. Saving the transport to/from the TSR. Also I could make a bolted assembly and it would work out to... But some objects would not work out if you didn't TSR and they will be a source of great frustration and rework... experience and budget drive many of these decisions (or maybe better to call them delusions)... Peter

Hey Momentz - Have you released your Lanko casting yet? Peter

Yep

Sent from my SM-G781B using Tapatalk

[joeavaerage]

Hi,
well I think I may have just shot myself in the foot. I had the cash lined up to cast a headstock in grey iron, and enough left over to get a good start on a new electrical cabinet.....
but the the bloody Buy Now button on Ebay has put paid to that!.

I saw a new spindle. Its a Chinese made spindle, 100mm diameter, 3.5kW (cont), 400V, 40,000rpm max with an HSK 32 ATC....with 10 HSK 32 ER20 toolholders included
and shipping to New Zealand for $2000USD.

I always knew I would have to replace my little 800W 24000 rpm spindle, I've been using it for years, and I use it daily for work. I'd go broke without it. I didn't really need more rpm, 24000 is
enough for most purposes, and I didn't really need more power, I seldom tax the 800W I've already got, but I did want ATC. This spindle has a lot more than I need but its the HSK32 ATC which
really sold me. The other thing is that this spindle has 3.3Nm of torque from down low, say 1500rpm. So that does not make it a 'steel spindle' but its a lot better than my little spindle. 3.3Nm should be enough
for 8mm, maybe even 10mm (light cuts) in low carbon steel.

Craig

[catahoula]

Sweet spindle and a good price for sure

Sounds like you're going to have to try stress relieving welded steel in a pottery kiln At least it's a smallish part

[joeavaerage]

Hi,
the cast iron headstock is an improvement I want to make, the electrical cabinet is an improvement I want to make, but neither improvement stops
me from using the machine.

I knew at some stage I was going to have to replace my little spindle, my business depends on the work that it does. I don't really need extra power or extra RPM but what I did want,
and have convinced myself I need, is ATC. Using that a selection process about the cheapest spindle from a known and credible manufacturer was 1.5kW, 24000 rpm and ISO 20
tool interface. They are all in the region of $1000USD to $1200USD, with slightly more powerful spindles say 2.2kW to 2.5kW around $1300USD to $1700USD. These prices exclude
shipping.

Thiis spindle (previously pictured) is 3.5kW (cont) and 6kW overload. This is quite a step up in power, and more importantly torque. Its rated torque is 3.34Nm, whereas my little spindle is 0.3Nm, a ten-fold increase.
So while I would not call this new spindle an ideal candidate for steel, it's certainly a big step in the right direction, I am anticipating I'll have the torque to run 8mm with ease, 10mm cautiously and 12mm
with very light cuts.

This spindles rated speed is 10,000rpm, but its maximum speed is 40,000rpm. So for those few occasions where I wish my existing spindle would go faster than its 24000rpm I now have that capacity. In truth
I expect that portion of its envelope to be little used. More importantly if its rated speed is 10,000rpm then its comfortable 1/2 speed is 5,000 rpm. Its not generally recommended to go much less than 1/2 speed
but I have done considerable cutting at 1/4 speed with my little spindle, and I expect this one to be very much more tolerant, ie 2500rpm. That in turn opens up opportunities to use bigger tools.
In short, this spindle I expect to have a much wider practical RPM range than my current little spindle.

I also like the HSK tool interface. HSK is certainly recommended at high speeds, indeed high speed operation was the major motivation for the HSK design. So while ISO20 or ISO25 would be fine for 24000 rpm,
they start to look a little marginal at 40,000rpm. Additionally ISO20 and ISO25 are fairly small (20mm and 25mm respectively) and might be expected to flex under the cutting loads I expect to engage in. HSK 32
on the other hand is bigger (32mm naturally enough) and as the first moment of area increases with the square of the radius HSK is therefore quite a bit stiffer. Typically, the smaller HSK tool interfaces (25, 32, and 40) attract
quite a price premium. So, to find an HSK tool interface at such a little price premium over either ISO20 or ISO 25 or BT30 is very hard to ignore. Especially as the seller popped in ten HSK32E to ER20 toolhoders,
very generous indeed, for free.

I have found that you can buy HSK32 in shrink fit. The most common sizes are 4mm, 6mm, 8mm and 10mm at reasonable prices, say up to $150USD each. I have found a couple of suppliers who have HSK32
shrink fit to 1/8th inch. These would be perfect for my PCB making tools but are some hundreds of dollars each!!! Yikes!!! RegoFix, (Swiss made) are up to 200 to 300 Swiss francs.....Must say it does
make me appreciate that this Vietnamese chap has thrown is ten HSK23 to ER20 toolholders for free.

Last thing is that the price includes shipping to New Zealand, again very generous of the supplier. In my emails with him, he is himself a DIY CNC aficionado, and he has treated me very generously indeed.
I already have the Fedex tracking number, so fingers crossed. If, and I am assuming here, that all goes well I feel very inclined to post a like to his site, as there are some very interesting items listed.

I've been waiting two years to make a new headstock and electrical cabinet, if I have to postpone them for a while then that's OK.

Craig

[peteeng]

Seems the zone is doing its double thing again... Peter

[joeavaerage]

Hi peteeng,
I live rurally and my internet is wireless and always pretty patchy from home. It's getting worse, and especially as now all the kids are off school.
It's difficult for me to tell when the CNCZone servers are playing up or whether its my own provider.

Strongly contemplating Starlink early next year.....although I've just blown my budget up...so it may have to wait. Reading is still free.

Craig

[peteeng]

Hi Craig - We are rural also and have awful to moderate internet. Late last year went Starlink and its great. Now I just have to solve the occasional power outages. Peter