Thread: First steel diy CNC router build

1. Wow, that's a handy website not just for cnc!

Couldn't find many cnc's using timing belts for synchronising axis. So I attached what I came up with.

So the beech colored ones are P32-5M-15F (32T) and the green one is attached to stepper using P18-5M-15F (18T)
If my calculations is right I need around 2380mm of 15mm 5mm HTD timing belt.
A = 940mm
B1 = B2 = R*pi = 50.93*pi = 160mm (assuming half of the belt is on the pulley)
C1 = C2 = 430mm
D1 = D2 = 0.5*R*pi = 0.5*25.46*pi = 40mm (assuming 1/4 of the belt is on the pulley)
E1 = E2 = 50mm
F = R*pi = 25.46*pi = 80mm (assuming half of the belt is on the pulley)
So the total length: A+2*B1+2*C1+2*D1+2*E1+F = 2380mm

The problem is that there are only 2525mm or 2000mm available from here. So I guess I will have to fiddle a bit.
And does anyone knows where to get these rotating pulleys (purple on drawing), at least the proper name for them?

On the side note:
I am about to purchase ballscrews and rails from Chai, just want to make sure I have not forgotten anything:

SBR20-700/900mm(4 supported rails+8 SBR20UU blocks)
DFH15 profiled rails 2x400mm+4blocks
3pcs Anti backlsh ballscrews RM1605-450/750/950mm-C7(3screws+3ballnuts+3end machining)
+1 anti backlsh ballscrews RM1605 950mm - C7(ballnut + end machining)
4PCS NUT HOUSINGS/BRACKESTS(Made of Steel) FOR THESE 4 BALLNUTS
+ 4 set of BK/BF12 with locknuts and circlips
+ 2pc 6.35mm*10mm flexible couplings.

Thanks again.
Last edited by ivars211; 17-04-2014 at 01:31 AM.

2. sorry, delete this.
Last edited by ivars211; 17-04-2014 at 06:03 PM.

3. Originally Posted by ivars211
Sorry for double post. As I couldn't sleep, I finished x and y axis. I need some approval from clever people, so that I can continue. I also realised that I have no proper bench to put my machine anyway, so I will most likely end up welding also that.
Have you thought about how you are going to mount the rail blocks to the frame, for instance the X rail blocks appear to be mounted to the gantry without access to the bolts. I would also wait until the clever people check your frame out and lack of table I noticed that you are ordering 5mm screws all round!! just bringing this to your attention ..Clive
Last edited by Clive S; 17-04-2014 at 09:00 AM.

4. EDIT: ok I realised I want the frame to be as simple as possible, so 100x50 steel box sections for Y axis makes more sense. Those white plates are supposed to be aluminium 20mm thick. Ignore the missing underneath structure.
Anyway, this is what I came up with after ~14h of browsing through hell lot of designs. Feel free to comment on any mistakes.
P.S. Never thought that design itself would take up so much time.
Last edited by ivars211; 17-04-2014 at 07:12 PM.

5. Hello, I just wanted to ask quick question, is ~35kg gantry too heavy for two nema23 435oz? Does weight even matter so much? Tried to look up on google, but without success.
Last edited by ivars211; 22-04-2014 at 09:54 AM.

6. Originally Posted by ivars211
Hello, I just wanted to ask quick question, is ~35kg gantry too heavy for two nema23 435oz? Does weight even matter so much? Tried to look up on google, but without success.
You're looking at things the wrong way round. Design the gantry to be as strong as you need, then get motors to suit. If the gantry ends up too weak due to lightening it to suit particularly motors, then the machine is arguably no longer any use to you.

The 35kg isn't a problem - the inertia of all the pulleys will be more than the gantry. See these threads:

http://www.mycncuk.com/forums/machin...do-i-need.html
http://www.mycncuk.com/forums/machin...do-i-need.html

The latter was intended for servos, but the formulas to find the required torque obviously don't change so you can use that to calculate the torque required for each axis and compare this to the motor torque vs speed curve.

P.S: Listen to Clive regarding the ballscrews.
Last edited by Jonathan; 22-04-2014 at 11:17 AM.

7. The Following User Says Thank You to Jonathan For This Useful Post:

8. Ok, just received steel boxes cut to size. Question is, what's the optimum bolt size to use? I have 3mm thick steel to play with, M6 sounds about right, or maybe I need M8? I tried googling it, but either my keywords were wrong or there is no information about it.
Last edited by ivars211; 21-05-2014 at 04:02 PM.

9. the optimum bolt size is the one that gives sufficient thread. generally you need at least 3 threads. so M6 x 1 will just give you 3, M8 x 1.25 will only give 2, so M6 but you'll need more of them to withstand shear & twisting forces. What many people do is use a 3mm plate inside the box section to add thickness so a bigger dia bolt can be used, ideally welded in place..
.
Also if you're bolting across the box section you'll need some tubing to stop the box being crushed...
Last edited by irving2008; 21-05-2014 at 06:22 PM.

10. The Following User Says Thank You to irving2008 For This Useful Post:

11. Originally Posted by irving2008
What many people do is use a 3mm plate inside the box section to add thickness so a bigger dia bolt can be used, ideally welded in place..
I used Gorilla glue to fasten a piece of 6x30 flat bar inside a 3mm thick box section and it worked great, Gorilla Glue UK | GLUES | GLUE LIST | Gorilla Glue
While I agree with Irving's post about thread sizes, I find a good method is to look at nut thickness dimensions for any bolt size and use that as a guide to how much thread depth is required.
Last edited by EddyCurrent; 22-05-2014 at 09:50 PM.

12. Eddy, that's a good rule of thumb and one I should have thought of!

Here's a good site for all such things:

http://www.roymech.co.uk/

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