8x4 Build based on plans by Joescnc Hybrid R&P

[GrahamWhite]

Yes I have to agree with you:( lol
although it's not so much of a problem now that I have to modify it for the ballscrew anyway.
I'll probably do a quick fix for the vee bearings to make sure on clearances and then the first decent mod. i'll redo the Z.
Would supported round rail be an option over the vee bearings?
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I've gone for SBR16 rail- looking at a few z axis they seem to be built with the idea I have in mind
Also got the 84mm long bearings so plenty of stability I hope
All mounted on 19mmx 90mm 6062 ali plate with 6" piece crossways for the spindle mount
This option works with the X axis as I have bearings studs through the front face so hopefully I can make it work

[JAZZCNC]

Would supported round rail be an option over the vee bearings?
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I've gone for SBR16 rail- looking at a few z axis they seem to be built with the idea I have in mind
Also got the 84mm long bearings so plenty of stability I hope

Yep that will be lot better than V bearings. Just make it strong.

[GrahamWhite]

So I've ordered my spindle -was going to go for air cooled as I didn't want the hassle of water pipes and pump but the breakout board I will be using has a dedicated pump relay built in so no real issues there!
Also they seem very quite and the price was right as well- seems to be a shop that just sells loads of items in bulk so undercuts everyone else selling the same stuff.
https://www.ebay.co.uk/itm/272749081...m=272749081454
That's the spindle,vfd,pump,water pipe,spindle mount and 1-13mm collet set! £238 delivered from Germany so no import fees unlike my pinion drive plates-just cost me £65 import fees this morning!

[JAZZCNC]

Suggest you don't use the Relay on BOB and save for something else. Instead, use the Relay built into the VFD.
Reason to not use it is to keep potential Noise away from the BOB where it's more vulnerable to interference.

[GrahamWhite]

I spoke to cnc4you today and they suggested for rack and pinion instead of running nema23's 4Nm with 3:1 reduction I could have just gone with 34's at 8.7Nm and run them direct or fit a larger pinion for slower speed??? would that be the same?

[JAZZCNC]

I spoke to cnc4you today and they suggested for rack and pinion instead of running nema23's 4Nm with 3:1 reduction I could have just gone with 34's at 8.7Nm and run them direct or fit a larger pinion for slower speed??? would that be the same?

Bad advise for several reasons and just shows how little experience CNC4YOU have.!
#1 The resonance directly on the motors will play havoc with the drives causing rough running. It will also Kill the motor bearings quick time.
#2 Bigger pinion will make go faster not slower.
#3 Bigger pinion will reduce resolution.

The reason for the ratio is two-fold.
#1 To increase resolution. Even a small pinion of say 15T (Mod1) will have a pitch of 47mm which is too high and will give a low resolution. It will go like the clappers but resolution or in simpler terms Smoothness will be rubbish and this shows in the cut. You want to aim for pitch between 10mm-20mm Max.
The CnC-router parts pinion I believe is 1" or if Mod 1 will be 25T which will give pitch of roughly 78.5mm with 3:1 ratio this brings down to 26mm which is still little high for me if want to do very detailed work.

#2 It increases the motor torque which is required to overcome the inefficiency of R&P.

Also, the belts help lower Resonance which affects motor/drive performance. DONT under estimate Resonance because it will and DOES cripple machines performance. This is why you'll often see recommend Digital drives because they handle Res so much better, but still they have limits and Direct driving R&P off the motor would challenge them and your abilty to tune the resonance out.

Edit: Just to go little further on why direct drive is bad idea and pinion sizes etc.
When using a machine it's important that you spec your components so that you have best performance while cutting. One important consideration with stepper based machine is that you aim to be cutting in the motors RPM range which gives best performace while cutting.

So if you have direct drive with big pinion and say your feed is low becasue say doing 3D work, then your problems start to multiply because now your motors are hardly turning. This scenario puts the motors/drives in place which isn't always good.!
Yes torque will be higher but do really need it while going slow.? However motor smoothness will suffer and this will often show in the finished cut which very much matters on say 3D work. OR affect the drives thru resonance causing rough running and others problems.

Hope this helps.

[GrahamWhite]

Ok Thanks ,so I have gone the sort of correct ish route!