[ardenum2]

Hi,
well you may not think they are suitable for you but they are to me. In truth both are probably a little large but otherwise they are what I want.
Indeed the fourth axis I have built is a somewhat smaller version of exactly the same thing. My fourth axis has over 40Nm torque, and that is a fraction of
the gearboxes rated torque of 130Nm. My fourth axis does not have a brake, but then I anticipate the majority use will be for continuous fourth axis
rotation, not indexing.



News flash, heavy duty fourth and fifth axes are uber expensive, tens of thousands of dollars. If you want a fourth and/or fifth axis of the rigidity to do steel parts, even
small steel parts you had best get used to the idea it's going to cost. How do I know?....I've been looking for three years. I believe I've come up with the most rigid combination
I could within my budget....at this time about $5000NZD ($3000USD). A good (Taiwanese made....not Japanese...they are more again) 4 inch self centering vice is $600USD on its own.
I'm not quite sure how you go about pricing things....I tend to look at manufacturers websites, enquire via email, look on Ebay for second hand or new old stock, but I always seem to come
up with an answer that you think too high. If you can buy as cheap as you claim then do so.....and tell us all where and how.

Craig

what the price is on the market is irrelevant. most high end products are overpriced because the manufacturer can get away with it or they became stale and use old machines/processes that result in funny prices. those kinds of prices are not for regular people, they are aimed at companies.

as for the stiffness in rotaries, it all comes from the bearing, YRT bearings which are arguably the stiffest bearings on the planet start at $150 for the smallest one, china sourced(eg. Luoyang Yujie). cheap, accessible stiffness is there. how you power the rotary is up to the individual preference.

[joeavaerage]

Hi,
it very much depends on the size of the part.

Lets say a part with a diameter of 100mm, and a target cutting speed of 1000mm/min, then a rotational speed of only 3rpm would secure that.
If the part is 5mm in diameter that equates to 63rpm. If your target cutting speed goes up, so inevitably does the required rotational speed.

I've posted what I believe to be the best combination for me. What fourth and fifth axis speeds is your machine capable of? What sort of toolpaths do you favor,
3+2 or simultaneous 5 axis? What CAM do you use to get your toolpaths? How would you describe the rigidity of your four/five axis setup? Can it for instance do steel
comfortably or does it struggle with rigidity or rather the lack of? What did your four/five axis cost you?

There are so many variables when you get down to it...what suits me will be inadequate for someone else, just as the speed that I want would be superfluous to someone else.

Craig

[joeavaerage]

Hi,

what the price is on the market is irrelevant.

BS The price on the market is irrelevant???? Unbelievable. The price on the market is what you can buy for a given sum of money. You may have noticed that all the rotary tables in that
'entry level industrial class' are many thousands new, and still quite some thousands when second hand. Do you suppose I would have bothered to make my own if I could have afforded one????
The whole point of me making my own is that I CAN NOT AFFORD THE MARKET PRICE, and your wishful thinking makes them no cheaper.

Do you ask 'for the regular people price' when you buy something, or do you argue if you think they have quoted the 'to another company price'?

Craig

[ardenum2]

Do you ask 'for the regular people price' when you buy something, or do you argue if you think they have quoted the 'to another company price?

I decide what a product is worth to me not some company. If I get a funny quote I just ignore that company from there on, put it into the 'thieves and scammers' category never to bother with it again. majority of all the products on the market are overpriced and have sh*t quality. I simply don't let myself be taken advantage off by ceos that pay themselves tens of millions while their engineers barely make a decent paycheck.

a situation is best analyzed by its extremes. If you woke up tomorrow to find out your politicians passed a law that puts a tax on the amount of air you breathe, would you pay it? because I'd make myself comfortable and spend the rest of my life in jail for not paying it.

[Buoyen]

Agree

Compare the UMC350 HD vs the non-HD and there are big differences in both speed and torque capabilities

[joeavaerage]

Hi Buoyen,
that is an interesting find, and it certainly highlights the difference between models.

It is certainly apparent that the slower model has way more torque, including brake torque, and would guess that it is highly suited to
3+2 type toolpaths. That is what I would expect for a 'tombstone' type production machine, whereas the faster model would be highly suitable for
simultaneous 5 axis toolpaths.

Craig

[ardenum2]

well a new video just dropped, the servo drives two helical pinions via a belt that drive a slewing ring with helical teeth gear on the outside. the pinions are also synchronized with each other with secondary gears. case closed

https://www.youtube.com/watch?v=q7MK1pgdcoo

[joeavaerage]

Hi Ardenum,
the same company that make my servo reducers that I'm using as fourth and fifth axis gearboxes have a similar system for rack and pinion
drives.

There are two pinions and driven such that they take up the lash in the rack....very clever. The simple system is where one pinion is torsional spring loaded against
the master pinion whereas the more sophisticated system has two independently driven pinions. Last word in lash control...not cheap but beautifully designed and
built.

Craig

[joeavaerage]

Hi peteeng,
I have a suggestion. A while ago (several months) I bought a modest worm drive for a retrofit that I'm doing for a friend. Its cheap, and has way too much lash
for a rotary axis, but was none-the-less very useful. Were you to buy such a unit you could then first hand asses the designs applicability to a CNC rotary axis. For the 'real deal'
you'd want a rather better and more expensive unit, but as an experiment a cheap unit like this could be very instructive.

https://www.ebay.com/itm/224805292521

Craig

[peteeng]

Hi Craig - Thks for the suggestion but it's way too robust for what I have envisaged. My starting point was a precision planetary like here:

Precision Planetary Geared Stepper Motor - StepperOnline (omc-stepperonline.com)

They come in 5:1 10:1 and 20:1 50&100 so a few to choose from. Being a router its not that critical for precision they have a 0.8deg backlash. I have used 10:1 on a small router and they are really grunty!!

Plus being a 5 axis learner machine accuracy is not high on the must have list...I haven't worked thru the numbers yet. Been trying to get a handle on the slew bearings or harmonic drives. Plus getting Frankie out the door. Of which it left today!! So now I have space (workshop and head)\ to start the next build. I've decided it will be a mother machine to make smaller machines. X2.5m Y1.3m and Z450+mm its called Lanky as its a sideways machine. The 5 axis project will be in parallel as I figure out its gaps.... I've been away for a week and have to start the wheels turning again on a few things.... Peter

[joeavaerage]

Hi,

Been trying to get a handle on the slew bearings or harmonic drives.

They are great, but too damned expensive. Opposed tapered roller bearings and precision worm gears are, if selected carefully, are very usable accuracy and lash wise and rigid enough
without breaking the bank. The worm drive I linked to has about 1 maybe 2 degree of lash, but is remarkably rigid. All the bearings, housings, worm reducer is all built in....its pretty much
a bolt on component. The one I linked to is about 1/3 the size that I'm using and I have lash in the 1 - 2 arc min range, and all that tricky engineering and manufacturing is all done, pretty much bolt
it in place. Is it as good as crossed roller bearings and a harmonic drive?....well probably not....but is it good,and especially is it good enough....then yes......and a fraction of the price.

Craig

[peteeng]

Hey all - speaking of scraping - Peter

https://youtu.be/xatHPihJCpM

[ardenum2]

hey Pete, what about forged carbon fiber? didn't know it was a thing

https://www.youtube.com/watch?v=25PmqM24HEk

[peteeng]

Hi Ard - Commonly called compression moulding. I imported some short Carbon fibres from China some time ago and set this up as a panel test. Strength is good as per the video but stiffness is poor. The fibres do not stack well as they are fluffy. I hoped 1atm would be enough to sort it so I could use a vacuum bag approach but it resulted in poor fibre volume. If we're chasing 70-80GPa using std modulus carbon then stacking double bias or unidirectional is the only approach that will get the fibre volume and fibre orientation under control. I regularly get 80GPa at test for yacht masts so this is achievable. Aluminium is cheaper.... hence my interest in laminated aluminium.

One issue with CF (plus the cost issue) is that it is not available in heavy weight cloth (by the way do not use woven cloth, the "crimp" reduces its stiffness by half, use stitched cloth so the fibres are straight ) so using 300gsm cloth to make 20mm thick laminates means you need 67 layers. Not much fun with scissors and stacking. I used to do this for superyacht parts in NZ but that's many millions of $$$ projects so it's not an issue for them..... The woven cloth stacked randomly achieved 40GPa which is not bad but then concrete gets this out of a bag at far less cost just add water... Peter

[joeavaerage]

Hi peteeng,
I'm sort of surprised. I was always of the opinion that carbon fiber was 'stronger than steel'. I've used it extensively in boats, more as repair and alteration rather than new construction, and
in model aeroplanes. But the modulus is, if careful, only marginally better than aluminum?

I was contemplating carbon fiber if I ever go to build a third machine especially for PCBs and the small parts I make for business, but at E80......I rather think I prefer cast steel, E207.

Craig

[ardenum2]

thanks Pete that's good advice, I've never seen anyone use stitched cf, but woven I've have seen used extensively, especially in car parts, aesthetics wins I guess?

Craig, small parts and pcb's? I can see linear motors and monoblock aluminium parts in your future.

[peteeng]

Hi Craig - CF by itself is way stronger than steel. So a run of the mill std modulus carbon fibre has an E=230GPa and a tensile of 4900MPa way stronger than any steel. But then you put it in a laminate and this dilutes its properties. Depending on fibre direction, fibre volume, matrix strength etc etc you get a laminate property not a fibre property. To achieve E80 in CF you need to achieve very high fibre volumes using autoclaves or infusion. Plus you only get it in the main direction. The cross direction will only be around 10GPa so great for beams loaded on one direction. Its shear stiffness is down compared to aluminium as well. I think it would be useful in a gantry if you also moulded in all the other features so its a one piece unit. But I think all things considered aluminium is better as a machine part. Steel is 7800kg/m3 and is really heavy when you try to make something light. In many machine parts the stiffness outweighs the weight then you have to get into damping... input shaping fixes that....to a degree.

For high speed parts CF is 1500kg/m3 and AL is 2700kg/m3 so its an advantage there, as the part will be lighter. If I where a commercial machine builder I'd be using intermediate modulus or high modulus CF to get parts at E=160GPa... now your talking (but need the $$$)

Hi Ard - Yes woven cloth CF is highly prized for its appearance but its not much good structurally compared to other products. The grail hunt continues.... Peter

edit- The E80 CF laminates achieve flexural strengths and tensile strengths over 1000MPa so still stronger than most steels. compressive strengths are about 600MPa...


Ultimate tensile strength - Wikipedia

[joeavaerage]

Hi,

I've never seen anyone use stitched cf,

Yes I got some, quite a few years ago now, two 600gsm uni-ax carbon and one 450gsm kevlar ply stitched together. Was quite a major repair. Two plys of this stuff
on either side of a 6mm closed cell foam core. Then regular Eglass to bring it up to fair. Job came up nicely. The insurance company paid for the repair and then the customer
had me supply and fit a new Yanmar saildrive, another $30,000NZD worth. Good work if you can get it.

Craig, small parts and pcb's? I can see linear motors and monoblock aluminium parts in your future.

Yes, that could be so. 90% of my mill work is for my business and its all small parts. 200mm x 200mm x 200mm would be entirely adequate, and it that size linear servos would
be a slam dunk. Although I think I'd rather go to cast steel rather than aluminum. I know casting steel is expensive, but its just so damned rigid its hard to overlook.

It order for such a project to make any sense I would need a good spindle, and this is my choice, downside is that it cost 5700Euro and that was around COVID time, who knows what
it might be worth now?

Craig

PS Please disregard the datasheet for the smaller 800W 65mm spindle, that is that I'm using now and somehow I accidentally selected it to be uploaded. The one I want
is the 2.2kW 80mm 42000rpm HSK25 spindle.

[ardenum2]

they went ahead and built it

https://www.youtube.com/watch?v=YPc66pJoQuM

[jackjr-123]

Hi jack - At early stages they are bonded together. The rail is steel and the car is aluminium. This is about the correct relative stiffness when you look at the manufactures car stiffness data. If you do a search for car fe in this forum you should pick up detailed descriptions of how to model cars...

Hi Peter,

I could not find any threads about how to model these carriages correctly for FE analysis... Any pointers?
In Bamberg's thesis, he suggests modelling the cars with an equivalent Young's modulus between 2 and 8 GPa. A lot lower than aluminium, and IMO way too low. Did I miss something?

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