Build log at last

[Gregor]

I am starting to design the gantry and after reading the other build logs I think i will use Linear hiwin rails HGR20 or should i use HGR15 for the z axis?This is probably a stupid question but what is the difference between a HGH20CA carriage and a HGH20HA and could someone please confirm if the height off the carriage sitting on the rail is 30mm.Do you think I can use one ball screw on the Y axis or should i go with two? All advice much appreciated,
Cheers Greg

[Clive S]

Greg From what I believe HRG15 on the Z is more than strong enough but the problem is that it would make it very tight on space for the ball nut and you would have to cut more out of the plate to accommodate it. There is not much difference in price between the two.

In my opinion at 700mm wide you could get away with one screw depending what you want to cut.

[routercnc]

I have 15mm rails on the Z and wouldn't do it again - more like 20mm. Much stiffer and give better spacing to fit all the parts in.

I've always gone with 600mm max width for single ballscrew, above that twin ballscrews. One of my earlier machines was a single ballscrew at around 600mm wide and you could push on one leg of the gantry and move it a mm or 2 without much effort. In practice this was still surprisingly effective even in hardwoods cutting off to one side, but I'm sure it contributed to errors cutting aluminium. So it's close, and Clive is right in that it depends on what you want to cut, but I would say 2 ballscrews at 700mm for robustness personally.

HGH20CA etc usually refer to the carriage style - wide, long etc. so google it to be sure. Some people prefer the wide version for for the X bearings (which the gantry then sits on), where you often want a large area to connect into. Whereas on the Y and Z you need every mm so go for the standard/narrow ones.

[Gregor]

Thanks for the replies, So 20mm rails for the whole off the machine , flange carriages for the X axis and HGH20CA carriages for the Y and Z .Will go with the 2 ball screws even though i only intend to cut hard wood but just incase i ever need to cut aluminium. I have had ago at the gantry, really i just stole Jazzcnc L shape design,Hope he dosen't mind .the front profile is 120mmx60mm and the back profile is 60x60mm the end plates are 20mm plate.
Cheers Greg

[Boyan Silyavski]

I certainly like the double ball screw idea and placement, what i dont like is the possibility of adjustment and the fact that both end supports are enclosed by the frame. Make sure the ball screw assembly is shorter by 1-3mm than the distance needed and use a plate inbetween, so you could sand the plate and adjust accordingly, or use epoxy putty there, adjust and let it dry.

Just make sure you mount the rails perfectly, that will guide the ball screws and will greatly facilitate the final adjustments

[Gregor]

I know you shouldn't buy anything until I have the design finished but i have been offered 3 X AM882 drives for £110 would this be a good buy and work well for this machine, With my knowledge off electrics not great i want to keep the electrics as simple as possible .After reading some more build logs am i right in thinking that 1610 ballscrews all round would be ok for this machine with Nema 23 Stepper Motor 3Nm all round or Nema 23 Stepper Motor 4Nm?
Cheers Greg

[Clive S]

I know you shouldn't buy anything until I have the design finished but i have been offered 3 X AM882 drives for £110 would this be a good buy and work well for this machine, With my knowledge off electrics not great i want to keep the electrics as simple as possible .After reading some more build logs am i right in thinking that 1610 ballscrews all round would be ok for this machine with Nema 23 Stepper Motor 3Nm all round or Nema 23 Stepper Motor 4Nm?
Cheers Greg

Greg If the am882 drives are in good condition then they will be fine . 1610 on X and Y. 1605 on Z nema 23 are good as long as you get them with low inductance the 8 wire version. Zapp or cnc4you have the correct one's