[ardenum]

Hope this helps. I have not found a simple one doc answer for all of this. Maybe I do a Phd on it... Peter

Blimey, I did not expect this amount of information, helps more than enough, thanks. Actually the frame stiffness is all right I think it was in range 40-60N/um last time I did FEA.

The issue at present was enough torque in the C axis actuator so it can handle a load of 1000N in simultaneous 5 axis operations. With the longest tool it is 100mm from the tip to the C axis center so given 1200N spec I had to have 120Nm actuator/reducer combo. But not enough space for current design attempt, in the headstock(see attachment).

I have to digest all this info and maybe try and find actual cutting loads data for HSM. researchgate here I come...

[peteeng]

Hi Ard - what software are you going to use for the 5 axis programming? Regards Peter

[peteeng]

Hi Ard - Just looked at Gwizard and it calculates the torque required in the conditions spec'ed. So from that you can estimate a force from the radius of the tool.... Peter

[ardenum]

Hi Ard - what software are you going to use for the 5 axis programming? Regards Peter

Mastercam or hypermill, but at this stage thats just hypothethical.

Hi Ard - Just looked at Gwizard and it calculates the torque required in the conditions spec'ed. So from that you can estimate a force from the radius of the tool.... Peter

sounds great, I'll check it out.

[peteeng]

Hi Ard - I investigated both of these about 12 years ago and back then Hypermill was so much better than mastercam but times change.... Also consider mechsoft much much cheaper and has full 5 axis functions. Peter

[peteeng]

Hi All - Milli's been a back burner project for a while now. Many things to do and only 10 fingers to do them. Here's the Porsche factory with many robots for your interest.

https://youtu.be/1YMJK-RPXpU

I'll try top get the CF test done asap that will give me some new direction. Peter

[peteeng]

Hi All- This looks like some good info on speeds and feeds. Peter

https://www.machiningdoctor.com/calc...chining-power/

[joeavaerage]

Hi,
36-26-36....just my favorite model robot.

Craig

[peteeng]

But Marilyn was 36-22-36 reportedly. I noticed one of the robots was called LEONI Peter

[peteeng]

Evening All CNC enlightened ones - to recap on Millis material. I have been looking for a material I can cold cast or vacuum cast that is as stiff as aluminium. I have imported some short fibre carbon fibre that can be dry poured into a mould then infused vs buying long fibres in cloth form. I made the billet mould today for the modulus test. A material supplier I use has offered to do the test which is great. So next is to seal the chipboard so it doesn't absorb its own weight in resin then prep the glass base and organise the consumables.

gas bottle - a little side project today for the workshop washroom. The shelf goes under the workshop next to the gas hot water system
mould on glass - this is what the infusion casting will look like. I'm going to use the short fibre and do a random cloth billet as well (hence 2 cavities). May as well get maximum info from the freebie test
ports done - first stage of the part is cutting the resin and vacuum port channels
tubing fit - checking the resin and vacuum tubing fit in as intended.

tomorrow I'll seal the frame and then start waxing the glass...

Peter

[peteeng]

Hi All - Came across this article again in some searching. Always good to revisit something like this. The closing statement is "When the system stiffness is high enough, says Mr. Singh, there is nothing left to damp" This machine is 350N/um stiffness, huge. So for all those trying to design machines and include damping they should be concentrating on making the machine stiff enough for their application then damping is solved. Peter

https://www.mmsonline.com/articles/a...e-for-titanium

[pippin88]

It's a nice quote Peter, but it is theoretical. Most of us inhabit reality.

He also notes that hydrostatic guideways provide damping (they damp much more than ball / roller bearings)

[pippin88]

"Dynamic properties of hybrid machine tool body – Theoretical and experimental investigation" - https://doi.org/10.2478/mme-2021-000
A paper where they filled cavities in a cast iron lathe bed with epoxy granite with improved damping.
Relevant as it has often been discussed whether filling a steel or aluminium tube with epoxy granite does anything. I have found multiple research papers that show it does improve damping, although the damping is not as high as a pure epoxy granite structure. I have not found a paper that shows no change in damping
for Damping: - epoxy granite > epoxy granite filled metal tube > metal tube alone
For stiffness: epoxy granite filled metal tube = metal tube alone > epoxy granite alone

"Lightweight heavy-duty CNC horizontal lathe based on particle damping materials" - https://doi.org/10.1016/j.ymssp.2020.107127
They incorporate particle dampers and nearly halve the weight of a large lathe (460 ton lathe), with an increase in natural frequency and a reduction in vibration.

.
I agree that maximising stiffness as much as possible is the first step. However there are real limits imposed by weight, materials, size of components etc that mean we will never achieve an infinite stiffness machine.

At present I think a hybrid approach may work quite well. A damp material (epoxy granite, UHPC etc) for the base / structure where size is not a major constraint. Stiff metal (or CF...) components where size is limited (saddle, head) with damping features incorporated (particle damper maybe).

[peteeng]

Hey Pippin - Welcome to 2022 may it be a great year for you. We have to have something to aim at and yes each design element has to be prioritized and understood. Each machine component probably has an optimum material/materials vs one material for all parts. We can't achieve infinite stiffness but we can achieve adequate stiffness. I'll look into the particle dampers... Thanks Peter

[pippin88]

Peter apologies if my first post (reality comment) came across poorly. I did not phrase it well and it's a bit abrupt and sarcastic (had a rough day).

There is some interesting stuff on particle dampers. Difficulty I find is widely varying results on optimal fill ratios etc. Some papers finding 50% fill with X size of Y material, and other 97%...
May need to be tuned to the individual machine / circumstance

[Buoyen]

I agree with Pippin that some hybrid frame of steel and UHPC/EG looks quite good.

Hydrostatic ways and drives is basically what Kern does, combined with their thermal control and "Kern Armorith" base material.

Question is if the hydrostatic ways is somewhat achievable for a hobby machine?

[peteeng]

Hi Bouyen - anything is possible at hobby level but the hydro bearings are a bit tricky. Look up air bearings this would be a good start. I have played with these a little and would like to make a router that uses them. Its easy with air as the bleed air goes to atmosphere so is clean. But with hydraulics you either need to collect the bleed oil somehow or you need near perfect seals to trap the oil entirely. At change of direction the pressure spike is very large and has to be managed somehow. But comes down to what your trying to achieve.

if you look at a 20mm std car its 65mm long. Its static failure load is 48kN. If you calculate the system pressure to support this load on a 20x65mm patch its 5333psi or 370bar or 37MPa. That's quite a lot of pressure so you need large areas to be equivalent to the std car strength. The std car is dimensioned for a useful life generally not its static strength. Since there is no contact in an air/oil bearing then its life is infinite compared to the rolling bearing type so a lower pressure would work but it has to be high enough to prevent contact and to present as a stiff spring... cheers Peter

[ardenum]

Question is if the hydrostatic ways is somewhat achievable for a hobby machine?

INA sells hydrostatic ways in size 45 only, not your typical boxway type guideway

https://www.schaeffler.com/remotemed..._149_en_en.pdf

"Lightweight heavy-duty CNC horizontal lathe based on particle damping materials" - https://doi.org/10.1016/j.ymssp.2020.107127
They incorporate particle dampers and nearly halve the weight of a large lathe (460 ton lathe), with an increase in natural frequency and a reduction in vibration.

If anyone needs full papers search on libgen.

[peteeng]

Morning All - Thanks Ard the hydro ways look good. Good to know they are out there commercially. They are very stiff as well at 5MPa pressure 50bar. Still a little high for my compressor. Peter

[ardenum]

Morning All - Thanks Ard the hydro ways look good. Good to know they are out there commercially. They are very stiff as well at 5MPa pressure 50bar. Still a little high for my compressor. Peter

fun fact kern micro hd has a unique hydrostatic guideway

.

I think they keep the whole assembly 'together' (starts at 2:28) by the vertical vector attraction from the linear motor because I can't see any type of mechanical structure to keep it together. Might just be a render thing though.