Quote Originally Posted by Fozz84 View Post
Totally agree with the low tooth contact area on the top pulley.

Would another idler wheel below the drive pulley be sufficient.... ... Say 180 degree + contact area.
Yes that would work better.

A
Quote Originally Posted by Fozz84 View Post
lso I'm not familiar with the stepper drive power system you mentioned. I'm looking AT Chinese Hss86 closed loop DRIVES. To drive a nema 35.
If its a way to power them, is there a handy video available. ☺

Bear in mind the machine will be cutting ply, plastic sheet, wood and maybe a bit of aluminium.
Well you have a mixture of materials there that require different feed rates, ranging from less than 1000mm/min (Alu) to +9,000mm/min to cut correctly. So it becomes even more important you choose the drive system correctly.

Those drives will be limiting to the speed because they only allow a max of 100Vdc or 70Vac and with the required safety margin on the PSU of 10% you'll run them at around 90Vdc or 60Vac. So you'll be lucky if you get much more than 1000-1200Rpm before they saturate and stall, that's without any loads or friction.
In reality you'll have a usable RPM of around 700-800.
Now this depends on several variables and friction is a big one. So your twin pinion system is loading the friction up even higher, Rack n pinion is also very inefficient so a lot of power is wasted just overcoming this. These things along with other power robbing parts of the machine like Gantry mass, rail alignment, bearings etc all come into play to how well the motors perform.

I've seen it happen many, many times that people building 8x4 machines mismatch the motors and end up disappointed with performance or worse still suffering with stalling motors in the middle of jobs because R&P binds a little or crap gets in between teeth and the motors are on the edge regards torque so stall and screw up the job. Even worse is that they where cutting too slow with poor finish quality and excess tool wear any way because the machine is crippled by the motors/drives/voltage.

This is often why you don't see many 8x4 or 10 x 5 Diy machines finished and why you see so many on ebay etc selling part finished jobs or frames, gantrys, etc

It's a very very fine line between getting it right and getting it very wrong, your at the point of getting it very wrong.!

It's more expensive doing it correctly but it's a one time deal and actually cheaper in long run because you won't be wasting material, breaking tools and the cycle times will be shorter plus you get better finish and longer tool wear.
If your doing this to make money with the machine then the first piece of expensive plastic it screws up on will cost you more than the difference to do it correctly first time.!! . . And that's with out factoring in the time you lose cutting the job again and sorting the machine or worse still lowering feeds to compensate so increasing the cycle time.!

But I could be talking bullshit so feel free to ignore my advise because I'm sure your thinking " Well I've seen others using them.!" which is true, but they probably won't tell the truth or are happy to cut at a much reduced feed rate and don't care about tool wear or finish quality, which is crazy for a few £100 more on a machine costing £1000,s and with the potential to make 10s of £1000's.