[Diman]

Hi there folks!

Here I was, living quietly in Sweden, doing nothing.... surfin' small electronics forums...
One day out of the blue I decide - I need a CNC plasma.
And so I find this place, read a LOT, learn some too... (not everything got stuck after first read haha) - must say awesome place, very interesting builds some of you got here!

So I began the project with some solidworks designs (took me a month just to learn solidworks... yeah, i'm a bit slow haha ), some more research on different power transmission systems, linear motion systems, controllers, motors, software etcetera, etcetera...

So far I've settled for Gecko540 controller driving Kelling KL23H2100-35-4B 3.5A 381 oz. steppers, some sort of THC (not acquired yet) too
x-axis: dual steppers, sbr rails, belt-in-belt drive with 4:1 reduction
y-axis: rails not decided yet (leaning towards THK stuff), belt-in-belt 4:1
z-axis: maybe THK KR-20 or KR30 actuator... I was looking at some pre-made z-axis assemblies on ebay, there're some really affordable setups there.

So nothing out of ordinary, pretty standard setup.

Have an old chinese HF plasma which, from what i've read here, i probably will have to throw away and buy a decent hypertherm or equivalent





Progress so far:

frame is built out of an aluminum extrusion from some industry hoist (strange shape but it'll do)



I had to build corners out of steel tube and some sheets





mockup, it's going to be big ! Rails are SBR25



some stuff from automation technology


beginning of the gantry


belts and pulleys


Belts are HTD T5 for reduction and Breco T5 for drive
I will glue one belt to the support track and the drive belt will mesh with the stationary glued belt, so no stretching - ever !

fabbing some gantry drive block walls, damn it's a lot of holes to drill


Reduction pulley and drive pulley on an axis...


here I have a small problem. Reduction pulley (the big one) arrived pre-drilled to 8mm, I have piloted and reamed drive pulley to 8mm too, but it still not a press fit. both reduction and drive pulleys on both left and right axles spin freely on the shaft and there are no set screws in either pulleys. I need a way to either fix pulleys to the axle shaft or to each other. I'd rather avoid having to drill and tap pulleys for set screws myself, but I cannot find any other solution except for tig-welding them to each other. And I don't want to do that. any ideas ?


I will probably have x-axis ready and moving in a couple of weeks, waiting for bearings, pillow blocks and some small stuff. Shipping from China to Sweden takes forever

[rayoung]

The build looks good so far. If you have access to a lathe you could try knurling the area where the pulleys are going to enlarge the diameter slightly to create a press fit. I'm curious to see how you are doing the drive belt because I can't picture it in my head.

Ray

[steve123]

It looks like you are moving along quickly! I think I see a big problem with the design though. It looks like the gantry will twist and flex a lot! You can test it by clamping a twisting arm (a bar of some kind) to the middle of the beam, and apply torque. Watch the end of the twisting arm move! Look at this thread (not mine!) for a very solid design. http://www.cnczone.com/forums/diy_cn...-new-post.html Note the TWO beams.

Here is another thread where he used what turned out to be a too-thin steel beam. See post #49
http://www.cnczone.com/forums/cnc_wo...l_-_aus-2.html
I had recommended some brace triangles on the ends, but didn't realize that the beam was so thin! I think your small aluminum beam will also act like this.

-Steve

[Diman]

Thanks those threads were rather informative!

I agree, gantry of this size could possibly flex if I was building a router. Since I'm not, and there will be some additional stiffness provided by the rails and belt support profile, I not so worried.
On the other hand, there could be potential problem with poor stiffness of the gantry and the weight of the Z-axis assembly which theoretically could produce a small jerk in the kerf when rapidly changing cutting direction...

hmm... I'll go sit in my thinking-corner....

[Diman]

made both drive carriage blocks (or whatever they are called) this weekend



those aluminum distance sleeves were really hard to make to exactly the same length, but after some head scratching I used pipe cutter with some careful marking


Still haven't solved pulley to shaft fix....

now I need to focus on my new drill press - bought one this weekend after breaking my old one. it was inaccurate anyway - some holes in drive block plates got drilled at incorrect angle and i will have to move the hole locations and redrill ....

[Arthurmetal]

Maybel welding the two pulleys together is not such a bad idea if you can do it without melting the teeth.
The torgue between the two pulleys is quite large.
I recently added a toothed belt reduction to my table. 22 to 72 teeth gears on a 16mm shaft.
The torge on your 8 mm shaft is even bigger!
I had in each gear two 5 mm setscrews. I had to retighten the setsrews twice! Adding dents into the shafts where the setscrews could sink in.
The continuos back and forthe jerking of the pulleys just kill your setscrews.

regards, Arthur

[Diman]

hmm thanks for the warning

I don't have access to ac TIG, so I will have to find someone who does. But maybe I can find another way to join these pulleys together

[Diman]

worked on drive blocks today, got some more done.
It's a BIG difference to have access to a rigid fullsize drill press. Much more exact and easy to work with.

I drilled holes for bearings and pillow blocks, measured play and finally solved that pulley issue.

solution - 2 component epoxy.
So I've cut some small groves on pulley surfaces that will be coincident with my dremel, added a spacer and filled every cavity with epoxy. So pulleys are now glued to both the shaft and each other. I hope it'll hold. At work I have a fiberglass pulling wire /rodder we push into ducts and attach a cable and pull through. that same epoxy was used to repair this rod and it still holds for some serious pulling.

[Diman]

I am a bit concerned about my gantry... the weight of these drive blocks.. and rails and z-axle assembly (which I haven't bought yet) three motors, etcetera... it adds up pretty quickly...

Is there some general guidelines or calculations (I can't seem to find anything on my own...) that will allow me to approximate the maximum weight of my gantry, given the motor and reduction configuration I'm using. One would of course strive to keep the weight low but it'd be nice to know the upper limit
where the torque from drive blocks is no longer sufficient for quick direction changes and acceleration/deceleration.


Tom are you here, I need your advice here