I've built this machine 100 different times in my head!!!

[Iwant1]

This also allows different pulley sizes to be used without changing the belt, which could come in useful.

Thanks Jonathan, good advice as I will be putting larger pulleys on the motor side. Now I can do it with the same belt.

Yep going for Hiwin, as I can't find any suppliers of new THK or NSK. I'm using 20mm profile rails and the carriages have 4 rows of balls.

I've redrawn the motor mount, but decided not to go with a full plate on the back of the z axis. Just extra weight for the gantry to carry. Can be easily added later if needed.

[Jonathan]

Yep going for Hiwin, as I can't find any suppliers of new THK or NSK. I'm using 20mm profile rails and the carriages have 4 rows of balls.

15mm rails will be plenty strong enough. The load ratings of 15mm are several times what the machine will require... considering you were happy with round rails just a few days ago, I don't think there's much point using bigger than 15mm since the difference in stiffness between 15mm and 20mm profile rails is tiny compared to the difference between profile rails and round rails. Many much larger industrial machines use 15mm rails.

I've redrawn the motor mount, but decided not to go with a full plate on the back of the z axis. Just extra weight for the gantry to carry. Can be easily added later if needed.

If you do add one it needn't be thick - 10mm would be fine as it's only to stop the joint between the plates that the Y and Z bearing blocks mount on bending.

[JAZZCNC]

If you do add one it needn't be thick - 10mm would be fine as it's only to stop the joint between the plates that the Y and Z bearing blocks mount on bending.

Know this is a bit late 3 weeks after posting but I've been asked for some input by Adil and was looking over the build again and spotted this comment.!!

Jonathan never have understood why you use this rear plate in the way you do because that rear plate on the back add's very little protection against the joint between Y axis bearing plate and Z axis rear plate bending in the vertical.?
The only forces that apply here are vertical force applied from one side and the overhang distance from the Y axis bearing plate to Z axis rear plate is nothing.? possibly few MM's. So the chances of that joint bending are zilch and if the forces were great enough to bend that then the rest of the frame and gantry are in big trouble and 99% sure something else would be bending/breaking much sooner.
Your design is an open ended box with very little strength in the vertical direction and if enough vertical force is applied at one side the other side will deflect in a similar manner.!

If you want to brace for that movement then plates on the side bolted into both plates would be much better and could be much thinner and still give far better bracing support than those backplates.? This back plate just add's weight and cost IMO for not enough gain and isn't required.!

[Jonathan]

The back plate is there because otherwise the Y-bearing mount plates are effectively cantilevered, hence in my opinion it's worth having something to reinforce these joints. However I agree that plates on the sides, as you suggest, would offer much better reinforcement, but this would increase the width of the Z-axis and loose some travel on Y, assuming the width of the Z-axis has already minimised. The plate certainly doesn't need to be the same thickness as the other parts, it was just convenient for the one in post #20 since I didn't have much of anything less than 20mm in stock, plus it was an easy way to support the motor mount.

Iwant1: How far are you with the design / build now?

[JAZZCNC]

The back plate is there because otherwise the Y-bearing mount plates are effectively cantilevered,

Not really much of a cantilever is it at 1 or 2mm and still your not supporting the cantilever but have created double cantilever ~(see-saw with bearings as pivot.!) with no bracing support.!!
Plate thickness doesn't matter could be 50mm or 5mm it's still adding very little vertical bracing support.? Plus it restricts the back side of the gantry so cable chain etc is more difficult to run.? . . . Like say IMO it's heavy, expensive, restrictive and unnecessary. . . Each to there own.!!!

[Iwant1]

Iwant1: How far are you with the design / build now?

Lots of changes have been made, its an ongoing process with every new thread on here, regarding motor drives and the strongest gantry designs. It gets so confusing. So far, I've managed to sell off my supported round rails and have already bought profiled rails for all axis, got a good price so went with 20mm. I also sold my 50v power supply and got a 2x24v toroidal coil from which I will build my 70v supply. And now I'm thinking about selling my pm752's for the digital am822's. I Know I know, I should have waited before I bought all the wrong components, but at the time, 2010, these were the most popular components. 2 years later I now want an even better machine than I originally thought of.

Anyway, I've also been busy buying all the electronics for my control cabinet. I will be using an old pc case, and filling it with goodies. Around £300 have been spent on all the electric bits, including screened cables, regular 16/0.2 cables, e-stops, limit and homing switches, relay gear, toriodal coil and electronics to rectify it, 12v and 24v psu's, small consumer unit, a selection of plugs and sockets, and the list goes on.

Chai a even sorted me out with a good price for a 2.2kw spindle and vfd, so I went and got some cooling components for this too. Mainly, a water pump with reservoir, double aluminium heat exchanger, 2 120mm pc fans and grills to go with the exchanger. Once these bit arrive, then I will see what size pvc hose I need.

I've been taking pic's of the control cabinet getting made and will post soon.

Adil

[WandrinAndy]

... I've ....... bought profiled rails for all axis, got a good price so went with 20mm ........ limit and homing switches...

I'm guessing that 20mm is kind of the norm for profile-rails and what Jazz for example has used on the majority of his machine pics?

How much space does one need to allow for limit switches?

[Iwant1]

How much space does one need to allow for limit switches?

Limit switches are quite small and can be put in most place, on the frame or moving parts like the gantry or z axis. I bought the regular small lever micro switches by Omron not the cheap unbranded ones.

But the homing switches, if you use good ones can be around 50mm x 50mm and 20mm thick, quite large. Again I went for Omron and got a good deal on ebay

[JAZZCNC]

I'm guessing that 20mm is kind of the norm for profile-rails and what Jazz for example has used on the majority of his machine pics?

Andy I only use 20mm because I get them for almost same money has 15mm so worth the few quid more. . . BUT they are massively over the top and 15mm would be far more than enough so use 15mm if you find some cheap.!

[Iwant1]

So, while away all the bits and pieces I ordered arrived behind me. It was like Christmas, opening all the parcels. I loved it.

Here are some pictures which I think will help others new cnc builders realise how many parts we need to buy.

The first picture is my control box layout inside of an old pc case. 12v, 24v and 70v psu are here along with drives, safety relays, discharge resister, BOB and fuse box.


My spindle and VFD were from Chai, unfortunately FedEX hit me with a 35 quid bill. I bought an er20 collet set, and full cooling setup consisting of double ali radiator, 2 fans, and a pump with reservoir. Just need to buy hoses and adapters. It was a great feeling powering the spindle for the first time.


This picture shows all the other components like switches, connectors, wiring, e-stops and lever connector blocks. Just forgot to put the cy screened cable in this photo.


Close up of switches and plugs. Andy, here you can see the difference in size between my 3 homing switches and 6 regular micro limit switches. The green push button is for the safety reset and round toggle switch is a limits bypass. The ones in the middle seemed a bit small so I bought larger ones which can be seen on the top left of the pic.


Adil