[suspension]

I am still looking for CNC milling workshops. Once I get their quote I may have to revisit the size.

I have calculated the total cost and it stands at around 8500 for now. This excludes machining. Some small but significant contributors to cost are motor brackets for 3 axis, ball screw bearings, ball nut bracket and couplers. I was wondering if I can sacrifice the quality (by using low cost chinese products for example) for the motor bracket, coupler and ball nut as these do not need to be of high precision? I believe ball screw bearings need to be high precision any way. Does this make sense?

[peteeng]

Hi Sus - Once you have a costed parts list you can make cost vs quality decisions. Cost down articles that do not affect precision. Try to balance out the quality of all parts so it's a commensurate design. It's tough but worth spending time on this aspect of the project. You can get the local machinist to do his best then manually tune the structure as needed. Although he has said his machine is 0.02mm? "accurate" it's more about repeatability then accuracy for doing lands and doing zero stress set ups. Especially from one side to the other ie a Z axis move at same height. I'm lucky where I am. I have good machinists with big machines, heat treat , painters, laser contractors and material suppliers no more than 2 hrs drive away for all of these. My current erk is that international freight has doubled in last year and seems there's no way around that.... so asian parts are now sort of costly. Still cheaper then local same parts but some are getting close due to local companies bringing in parts in volume and not being greedy with margins.... Peter

[suspension]

yes already doing that.
I can find information about 3 plates method to create surface plates. Was wondering if there are specific tutorials/videos that show how to make linear rail plates parallel to each other.

[peteeng]

Hi Sus - I have not done this myself but I have been involved with fairing racing boats and other expensive boats over the years. I also used to lap ultrasonic transducer plates to parallel. I have lapped my timber router walls that have high rails. The video on scraping shows a common error when working surfaces. Do not concentrate on one area only. The two surfaces have to be considered as one. You need a lap that can go across both lands. Levelling and fairing are averaging processes. You slowly work towards the best average condition. You have to decide if you are going to aim at averaging down to the lowest point or averaging to the average "height" then fill in the dips with epoxy. You use a contrast like engineers blue (auto paint supplies have a carbon dust contrast that's good on a pad) to show up the low points. Black spray paint is also used, just a dust coat.

So you make some flat laps that can span the two lands and are as long as possible. Say around half the land length or more. You would make these using the 3 plate method could be some steel plate 20mm thick needs to be heavy or cast from non shrink grout then level them after they are stable. Plus they need to accept grit paper or tape like silicon carbide paper. Start with a coarse paper 100G wipe this across the contrasted surfaces (wet and some detergent) and determine the low spots. Use the scraper to deal with very high spots only, be gentle. Work the 100g one way say across the lands only. When you have a consistent scratch across the lands, change directions along the lands and scratch more. If you have a dial guage measure the low (coloured) to high points (shiny) and decide how far you are going to go "down". Use an engineer's level to set up the part to nominal level. As the surfaces develop keep checking both sides and both directions are staying level. Once you have a good consistent scratch across and along with 100g and your lows are known, go to 200g. Or keep going with 100g until you get to the lowest height that you decided to get to. Epoxy will fill 0.1mm quite nicely so say you target the low to be 0.1mm under the high point. But at that point if its moving along nicely you may say lets keep going to the lowest point. So once you have the two surfaces with a consistent scratch across and along scratch with 100g and its level and both sides are the same height (project across with the eng level or dial guages and stands) then you go to 200g. More contrast more lapping. The tempo will speed up here as the surfaces are now close. Good scratch across and along with 200g, go to 400g then 600 then 800 then 1200 then 2000 now your extremely close... Only use the scraper to remove very high spots... Now if you decide to go this pathway do not have high registers or reference edges as then you can't lap across the surfaces. Have the lands proud of the part so there are no obstructions for lapping. Good luck... Peter also mark out where the rail holes will be. if you have a low at a bolt then you need to come down to that spot or fill with epoxy. If you have a low at a bolt the bolt will pull the rail down into the hollow. If you have hollows between bolts these can be filled with epoxy or you decide to come down to total metal flat. Depends on how well you are going with the process.... I'll research what size each grit is maybe 2000G is too far. 2000G is good for mirror finish on cars and boats but probably too much for this job... 400-600g maybe I'll find out....Peter

[peteeng]

Hi Sus - I looked in the Hiwin and PWI manuals and they do not spec the surface finish of the rail lands. Typical off the machine roughness is 3.2um maybe 1.6um (can a machinist verify this please, its an area I do not work in) say 3.2um is Ok then that's equivalent to a 40G paper. To me that's rough... anyhow that means of you finish at 80G thats 1.8um which is very good.... so I should also use the correct term for the grit. So coarse is P40,P50 or P60 medium is P60 or P80. P80 would be 1.8um so more than good. With the brass ultrasonic plates I started at 120, 200 and then 400, 600 and P800... with composite moulds we go to P2000 then give it a rouge polish.. Peter

[suspension]

Thanks Pete, very useful information. This is my last resort! Hopefully I will have the patience to do this.
I also encountered this website which seem to supply grounded plates for reasonable prices.

https://www.coventry-grinders.co.uk/...c-gauge-plate/

For example, a 10mm thick, 300mm wide, 500mm long grounded plate would cost 107 GPB. Looks like the maximum width is 300mm.
If I can keep rail gap for all three axis inside this 300 limit, I should be able to use such a plat?

What I an thinking is fixing this plate to the EG through several bolt heads. So bolts will have to be fixed to this plate which require threaded holes say from M16. (Would doing this screw the ground plate?). While doing this, I can create threaded holes for bolts of rails, motor brackets, bearings etc as well. This would only need a mill with limited precision.

Once this is done, I just fix rails, bearings, etc on the plate which is supposed to give the precision I need.

[ardenum2]

This is how it looks

[peteeng]

Hi Sus - If you start with a precision plate then ideally you cast in a pocket for that plate say 6-8mm deep. You then have a few holes M16 too big maybe M12 but the idea is to "float" the plate in the pocket on 3 small adjustment screws until its in correct position. Then you pour epoxy into the pocket around the plate to set it in position. Have a couple of largish holes to do this, one for pouring one for breathing. Then when set you can softly pull down a few of the big bolts. You can also settle the plate down on screws until correct, lift the plate fill with thickened stiffer epoxy putty (epoxy filled with metal for instance) then replace in same position, adjust then wait. But flat plate means you will need spacers for bearings or rails.... You could have plates machined with a gutter and holes etc and get to the same place. This will give you a bit of flexibility in size and geometry. If you go this path the metal will have to be a stress relieved variety so as it won't warp when machined. Discuss that approach with the machinist you feel confident with. Peter

addition - I expect 10mm too thin. It will be easy to distort with bolt tension. Maybe 30-40mm thick your gutter will be 16-20mm depends on your bearing type... Consider 50mm or 60mm thick aluminium. I realise its a different co-eff of expansion but your mill will be in a stable environment. This will make it lighter to handle. Is there an anodiser around? Peter

[peteeng]

Hi Sus - Some time ago I had a meeting with the machinist I use about making a mill. I had come to the conclusion if I'm going to take something to a machinist (cast concrete or EG blocks with metal inserts) then I may as well have as much as possible done at the machinist. The conclusion was to buy 75mm thick or 100mm thick aluminum blocks and machine them. Al is cheaper to machine then steel and does not need rust protection. The material company cuts the billet to shape for free and delivers for free, so I don't have to cart it there. I do have to cart it home but that's the good side of the task. The 75 and 100mm plate is the break point for cheaper aluminium. Over 100mm the $/kg jumps. Use 6061-T6 as it has been solution heat treated so is stress relieved. 5083-H32 is cold rolled and can change shape after machining. There are tooling grade alloys as well used for plastic injection moulding moulds. Aluminium is same stiffness as granite and similar density. So find a machinist that your comfortable with and maybe this is a good pathway. If your going to have plates milled to spec may as well have billets milled to spec.... We then hit the machinists biggest size limit which was 800x300mm so then that put me down the plate build path with edge bolting and dowels for bigger machines. This would suit a gantry high rail design like I build in plywood. Peter

[joeavaerage]

Hi,
bang for your buck its still hard to beat steel. 205GPa Youngs Modulus, three times that of granite or aluminum and double that of grey cast iron

There are many places that profile cut, either with plasma or laser. Here in New Zealand it works out to about $6NZD/kg (about3GBP/kg).
If you want to machine the edges square it can be done but it costs. Otherwise just grind (with an angle grinder) the edges, cheap and cheerful.
Put the whole thing in a surface grinder and for 100GBP it comes out smooth, flat and top and bottom surface parallel to within a few um.
Whats not to like about it?

Craig

[peteeng]

simples - the mass. Peter

[joeavaerage]

Hi,
but you guys are talking casting in concrete or some variation of it....is concrete not heavy?.

Anyway I said 'bang for your buck'......so I was concerned to get the stiffest result for the least money, and steel still heads that list.

Craig

[peteeng]

Hi Craig - That depends - Take a machine base in a C machine config. That means the base is in bending. So if I have a 100mm thick aluminium base the same rigidity steel base would be 70mm thick. The steel base would weigh 546kg/m2 the al one would weigh 270kg/m2. So is 546kg of steel cheaper then 270kg of al and can that steel base be managed thru the machining? I don't know without talking to suppliers etc.

By the way most of our OZ local thick aluminium comes from Russia and I'm told local stocks are about to run out so we are about to hit an AL cost rise and shortage. So I expect steel wins very soon...

Now if I use 50GPa concrete the thickness is 112mm and its areal mass is 257kg/m2 so maybe grout is attractive & the winner... Peter

[joeavaerage]

Hi,
here thick sections of tooling grade AL are $14NZD/kg. It has been a while since I checked but that made it more expensive than steel for a given stiffness.

Today, in fact while I've been typing, I've just had a price from a plate supplier to supply a 360mm x 260mm x 32mm med tensile steel plate and two 260mm x 160mm x 20mm
med tensile steel plates for my trunnion table and the total cost is $242.81 NZD including GST. That works out to $6.56NZD/kg, which includes the profile cutting, the steel material itself
and the local GST. The company is about 350m away.....I'll pay on-line now and it will be ready for me to collect tomorrow.

Aluminum has some things to recommend itself but for a given stiffness for minimum sum of money steel is still supreme.

You might think casting in grout is cheaper....until it comes time to load it into a machine for facing, grinding, milling or whatever.

In 2021 1.9 billion tonnes of steel was consumed worldwide, that is 250kg for every man, woman and child on the planet. That little toddler you saw at the supermarket this morning
will on average consume ten times his body mass in steel this year alone....whats he going to do with it all do you suppose? Steel is, and remains, humanities premier engineering material,
and I'm not going to try to swim against the current.

Craig

[suspension]

Few more questions as usual

1. I am bit unclear about the process Pete describes to attach the plate to EG. In any case, wouldn't this method create a plat that rests on soft epoxy? This would be a problem with Z axix as it wont move with any movement on table.
2. Why cant I attach this plate to EG base using same mechanics to attach individual steel plates? (In Stef's and Badhabit's build).
3. If I am to use a plate would normal concrete work as shrinking may not be a huge issue? (As the plate wont shrink?). For this to be effective I may have to have a bigger plate so that column can also be mounted on the same plate.
4. Would the accuracy of the plate be altered if I were to mill holes for EG attachments and rail attachments.

Thanks

[peteeng]

Hi Sus -
1) Yes but the epoxy would be very thin (<1mm) and the plate is supported in a pocket. There are many machines in the forum that have had their column corrected using an epoxy bed. Everything is a compromise once you can't machine something
2) You can , you need to make decisions
3) Depends on the material and the holes, again you need to make some decisions set a course and get going. Peter

[ardenum2]

If I am to use a plate would normal concrete work as shrinking may not be a huge issue? (As the plate wont shrink?). For this to be effective I may have to have a bigger plate so that column can also be mounted on the same plate.

never use regular concrete
never use leveling epoxy under the rails.

[peteeng]

Hi Sus - Normal Portland cement based concrete shrinks (shrinkage of materials is the hugest problem machine builders face with all materials), Portland cracks and changes shape over months and many years. Its not the thing to use for machine parts. You need materials that are dimensionally stable. Peter

Hi Craig if steel is $7/kg and Al is $14/kg in Kiwi then 100mm of al 1m2 is $3780 and the 70mm steel is $3828 same ? I'd go aluminium. I appreciate your married to the iron age, irons in our blood so our machines should be made from it!! some say. But I try to look at all the options. Peter

I buy the 3350 for $80 per 25kg bag which yeilds 24.6kg of grout. So this is $3.25/kg. So the 112mm slab would cost 257x3.25aud=$835 so its way ahead of the metals... Plus the sika is premium material. I could choose a cheaper class C grout at half the price so it would be less $$$ but thicker. if I used Lanko 701 class C grout (still made by sika and sold at Bunnings) at E=40GPa and cost is $1.85/kg then the 120mm slab weighs 276kg and costs $510 a real bargain... Thats why people are interested in concrete... the $3000 saved can go towards the machining and they can do this in their garage.... AND that's exactly why commercial machine builders are looking at it as well.

[ardenum2]

found a video on proper scraping, short strokes.

https://www.youtube.com/watch?v=JGYwJ3RQpQo

[suspension]

Looks like even big precision CNC machine manufacturers use hand scraping to get required accuracy:

https://www.youtube.com/watch?v=_e2aWlZKtGU
https://www.youtube.com/watch?v=fVQ7uXjXlH8