Milli a new composite mill kit

[ardenum2]

Go thicker. Won't increase the cost much.

it's not like you can choose the thickness, if you want a thicker plate, the size changes too, then it becomes too heavy.

[pippin88]

You can get custom thickness. I have a 900x600x200 plate. (I didn't organise it, got it as part of a group buy organised by someone else)

These plate manufacturers are often doing custom stuff. Lots of them make machine frames with inserts etc.

[peteeng]

Hi - If I buy Lanko 701 and make a 900x600x120 plate it would cost $450AUD and weigh 248kg. Grouts about 2300kg/m3 and granites about 3000kg/m3. Plus I'd cast a couple of laps say 500x300mm. 500x500 would be OK. Lapping is not "hard" as you don't have to lift the lap gravity does that for you, but it does take time. I have not lapped such a surface before but I have faired boat hulls and that is hard (working overhead with longboards is HARD) and time consuming. 4-5um is coarse grit so if I lapped to 120grit it would be 1.3um. I've watched videos of the plates being lapped in china and they use small laps on bungies and lots of time I expect. So If I cast my own plate I can get the size I want. I intent to cast a long table with self levelling concrete to make a surface for laminating gantries on. This will be a test case for the surface plate.... Peter

found the Moody paper on surface plates for peoples info

[peteeng]

Hi all - Maybe I can machine concrete after all...
Red Art Concrete CNC Pro Machine - Pro Tool Reviews

Peter

[ardenum2]

Found a technical manual of a dmu that has really good drawings of the ram.

https://www.mediafire.com/file/vm7ed...inear.pdf/file

[peteeng]

Hi All - following #1569 the CF sheets I made for a ukulele. Here's the main bits at the luthiers. He's impressed so far with the CF. But we wait until it makes some noise. Peter

[peteeng]

Hi All - Well the coupon results are in and they are disappointing. The alox sample was the stiffest at 18GPa, next was the aluminium epoxy at 12Gpa and last was the steel fibres at 7GPa. Results where nice and linear and flexural strengths were reasonable at 50-60MPa for all coupons. I expected the steel E to be low due to the very poor packing factor it achieves (volume ratio). So the UHPC is much better. I was hoping the aluminium would do much better. Since aluminium and sand are the same modulus I find it difficult to expect much better then this in epoxy granite... These were made via a vacuum casting process so are high quality castings. I think the compression testing results that most data use are test biased. Since we use the material in flexure this is a better representation of how it would work in practice. I'll look at the raw data a bit more then go buy some grout! I may ask the lab to do a compression test to see what that gives but on face value why spend the $$$ for an academic result. Maybe make flexure coupons from the grout maybe a better spend. So onward to designing grout machines and figuring out how to machine grout.... break out my diamonds.... or make infused fibreglass parts at 30GPa or CF at 70Gpa....Peter

[joeavaerage]

Hi,
bugger!! You'd hope for a better result than that!

If I'm interpreting the result correctly Alox is stiffest but also the weakest? And at 18GPa thats hardly that flash.

Craig

[peteeng]

Hi Craig - Yes ALOX is stiffest and weakest. But strong enough for machine parts. Now I have to figure out how to use up 25kg of alox and 18kg of steel fibres. Fillers maybe. Laminated metal is looking good....Peter

[joeavaerage]

Hi,
egg and breadcrumbs....hard to beat....washed down with metho and Coke.

Craig

[peteeng]

Hi Craig - The published flexural stiffness of formply is 17Gpa which I use a lot. I'll have to set up a test. Laminated ply and aluminium has proved to me to be very stiff.... Peter

[joeavaerage]

Hi,
I favour laminated cast iron, cast iron on the outside, cast iron in the middle,in fact cast in one piece seems to work really well, stiff as old boots!

Craig

[peteeng]

Hi Craig - We are aware of your small peccadillo with cast iron. One day you may awaken to other materials... Peter

[joeavaerage]

Hi peteeng,
well yes maybe....when other materials can come within a bulls roar of cast iron....that would be something to consider, as it stands for a given sum of money spent steel and
iron are still take some beating.

Craig

[ardenum2]

So onward to designing grout machines and figuring out how to machine grout

no magic there, gotta grind it hard

[peteeng]

Hi Ard - Seems carbide burrs are used alot for concrete. I shall have a go on Scoot.

I want to stay in one universe vs having large metal inserts etc, So threaded inserts are OK, drill a hole and epoxy in the insert... Flats will be cast on then final machined... I'll drop into the local stonemason and ask what he uses on his big cnc. Or maybe I'll bond on fibreglass slabs and mill them, I have done that before, but then may as well use aluminium.... I was hoping the AL/EP would do much better. Anyways good to have definitive info. Still some things up in the air will get into it and the answers will show up. I have started designing a 5 axis mill so will use this thread for that. Milli-5 Its a trunnion/rotary 5 axis like the Hermle. Sorting slew bearings at the moment... Peter

[ardenum2]

I have started designing a 5 axis mill so will use this thread for that. Milli-5 Its a trunnion/rotary 5 axis like the Hermle. Sorting slew bearings at the moment... Peter

https://lyyjindustry.en.alibaba.com/...2/Bearing.html

good prices, smallest YRT was $120 in 2020, prices may have gone up but these are beasts of stiffness. Due to their geometry and how you mount them they fit best for a rotary table too, at least seem that way to me based on a bunch of models I did over the years. You can also have them modified with a gear on the inside or outside if you want to drive them directly with a pinion. Only seen straight teeth but maybe they do helical. Clear and fast communication with the company too.

There's also RU cross roller bearing but its bigger and less stiff.

[peteeng]

Thanks will look thru those, integrated gearing is useful - I'm thinking of using unitised 4WD front bearings (generation 3 type) drive using the spline. NSK have design data. But they are "thicker" (75mm) than slew bearings so take up more space. I used 2 on a robot I built many years ago.... or "thin" bearings all up in the air at the moment.. But the answer will fall out soon...Peter

[joeavaerage]

Hi peteeng,
I worked as a mechanic for twenty years and have fitted more of those bearings than I care to think about. They are remarkably good, but I'm less sure
about their applicability to CNC.

The bearings are very strong and tough with superb impact resistance but even when fitted they have clearance, not much, but some. As you know meant bearings meant for high speed service have
clearance such that when they heat up they do not run an interference fit. Highly appropriate for automotive wheel bearings.

CNC bearings however run (commonly) preload so there is no movement. This has consequences on service speed and service life but is deemed an acceptable tradeoff.

Do the bearing manufacturers specify the clearance as assembled? Would such clearances be objectionable in a CNC machine?

Craig

[joeavaerage]

Hi peteeng,
as you know I have designed and am building both a fourth and fifth axis.

The height of the fifth axis is critical. The lower the profile of the fifth axis drive the better, it reduces the moment arm of the trunnion table, and thereby reduces the torque required
to just 'plain bloody hard' from 'just plain ridiculous'. To this end every mm shaved off the height of the fifth axis is 'money in the bank'.

Wheel bearings such as you have suggested are pretty good, 75mm stack height.

The worm servo reducer I'm using has two taper bearings, approx 120mm outside diameter. Clearly the rigidity of the axis is increased as the separartion between the bearings
increases, but only at the expense of the profile height. The servos reducer has an overall height of 130mm, which is not bad, and is delightfully rigid, but I wish I could reduce its
stack height, without any reduction in rigidity.

The bearings that Ardenum mentions are very good in that they tend to be very low profile, 20mm or so, and quite big diameter, 150mm or more. Consequently you can get a rigid axis
at reduced profile height. I think the performance benefit (rigidity/profile height) is so strong that it puts automotive wheel bearings out of contention no matter the price advantage.

Craig