A sufficiently strong machine

[Jonathan]

I have another question about your design.
The holes on the steel are for moving the bed up and down? So, how will you keep the original parallelism of the rails that move the gantry, shimming every time? Or using the supports i see on one of the pictures and shimming and adjusting in vertical position connecting the table to the supports instead directly to the steel frame?

The main reason for including an adjustable height bed is so that the machine can maintain sufficient rigidity whilst cutting tall and short parts. This machine is plenty strong enough to cut aluminium at a respectable rate even with Z-axis fully extended, so I don't think Sasha will be moving the bed at all often. When it is moved, it will either have to be skimmed or shimmed. Putting shims on the 7 aluminium support blocks that the bed mounts to is probably the easiest way. Also bear in mind the holes for mounting the bed were drilled accurately using my milling machine, so the error introduced by moving the bed should not be very large.

Just to be clear, changing the height of the bed only affects the parallelism of the rails with respect to the bed. The measurements of rail straightness (and twist) we took effectively subtracted the error due to the non-parallelism of the bed, as once the bed is skimmed using the machine this error will be largely eliminated.

About the epoxy. You mentioned the brand. Where did you get it from? Abroad? How much epoxy was used? I have to do this very soon.

It was from the UK - I contacted lots of different companies who sold similar resin to see if they could get the hardener. You might want to ask Clive S where he got his as he got some much more recently than I did. The company 'Desperate Measures LTD' quoted £24.48 for 1kg of resin and £17.61 for the hardener to go with it. I think those prices do not include VAT, but I'm not sure.
I think we used about 600g of resin - I can't remember exactly. You can work out what mass of resin you need by just working out the volume (remember to include the bridge across the middle) and multiplying by the density they quote. About 4-5mm thick should be plenty.

[Boyan Silyavski]

... The company 'Desperate Measures LTD' ...

You made my day.


Thanks again for the information.

[dazza]

Thats some thread mate,well you know im a fan of this machine,i saw it being built at various stages i used to stand there in awe lol just staring at it,its so busy,well done lads.

[george uk]

Hi

you could not have timed this better for me, am just about to start a build. I want quite a heave duty machine for milling stone/ally

Question. Would there be a benefit from using larger motors Nema 34s or 42s or might it be a problem

[Jonathan]

I want quite a heave duty machine for milling stone/ally

Question. Would there be a benefit from using larger motors Nema 34s or 42s or might it be a problem

For the machine in this thread, there would be no benefit - in fact it would probably make the machine worse. Larger stepper motors tend to not spin as fast, but output more torque. If the smaller motor can output sufficient torque to obtain the required aceleration and speed, there is therefore no point using a larger motor as it will just cost more and sometimes not go as fast.
You would have to be building a huge machine for Nema 42 motors to be the correct choice. See this thread for a more detailed explanation.

[george uk]

thanks, am reading that now. Brilliant stuff.

I have another 2 questions or request for your opinion.

1. To stiffen up Z and Y ( when in action together ), i was thinking off adding rails to the inside edge of the X top support. ( i may want to add an impact head to it in the future ). Any opinions ?

2. any idea when the files will be available, am eager to have a crack at this.

[Jonathan]

1. To stiffen up Z and Y ( when in action together ), i was thinking off adding rails to the inside edge of the X top support. ( i may want to add an impact head to it in the future ). Any opinions ?

It's hard enough to align 2 rails let alone four. If you really need the higher load ratings, it's easier to just use bigger rails.

2. any idea when the files will be available, am eager to have a crack at this.

Soon. Sasha's still sorting them out but he's more interested in making the enclosure for the machine at the moment!

- 2 x 100x100 steel box for the gantry

Could do, but clearly that makes getting an accurate surface to mount the rails on more difficult. An early design for this machine did use 60*60 box section, but we decided not to use it as aluminium is much easier to machine.

-The bearing blocks and rails on the gantry to be at the upper side/or at the lower side/ so i can use epoxy and level them easy

Definately lower side as you want to keep them as close to the bed as you can to minimize the overhang.

-2x ballscrews at the gantry near the rails

I presume you're referring to the Y-axis? If so then yes it will make a noticeable difference to the stiffness of the Y-axis, but bear in mind it's already exceptionally strong so it's by no means mandatory. You could achieve the same by increasing the spacing of the Y-axis bearing blocks quite significantly.

What worries me most is the Z, making the z box and adjusting rails and fitting everything in place there. maybe using some ready box section and fit the spindle inside and fix the bearing blocks to the sides of it.

We used separate plates as they can be adjusted to get the rails parallel. Also it means you can machine features inside the Z-axis and you're not restricted to limited standard sizes.