Steel framed fixed gantry draw slide build super cheap

[JAZZCNC]

Jazzcnc just the other day you said "No thanks got better things to do and couldn't give a shit anyway" in referral to my cnc draw slide build so my question for you is why are you still posting on this thread ?, since you are then give me a ballpark figure in Nm of the axial load range i can expect.

"Please explain/show the equipment you use to measure to that level of accuracy.!" https://en.wikipedia.org/wiki/Foucault_knife-edge_test

Because it's Free country and Forum so I can and there's sweet FA you can do about it other than not reply.! . . . . . . But It's true I don't give a shit what your doing however I was intrigued to how some one who thinks draw runners are suitable for CNC would go about measuring such fine tolerences.?

Oh and if going to quote try using the "Reply with Quote" button it's much clearer.

Regards Axial loads then like I say depends on lots of factors and lifes too short to waste time working it out plus I'm not that clever.

[Steel]

Ok so you don't really know about what axial loads i will encounter ok fair enough maybe someone else has some idea ?

[Zeeflyboy]

Axial force from the plunge is I would say largely irrelevant in the materials you are using and is probably the least of your worries. The weight of the router/mount and travelling parts of the Z-axis are probably higher than the force required from the motor as long as you aren't plunging crazy fast.

Typical max axial rated load for a double bearing nema23 is in the region of 1.5kg-f (e.g. see data sheet here, last page at the bottom specifically) https://www.anaheimautomation.com/ma...ec%20Sheet.pdf

So your biggest problem (in terms of Z-axis axial load, I think Jazz would probably contend that it's not your biggest problem lol) is that unless your screw, nut, router, router mount, and all "hung" mass of the mounting plate is less than 1.5kg, you are already exceeding the axial load before you even start moving.

Let's say you are using a small router that weighs about 3kg, add the weight of the screw, router mount, etc etc and what, maybe 5kg? Simply hanging there before taking into account any dynamic acceleration loads during retracts you are exceeding the rating by over 3 times.

You could bodge your way around it by counterweighting the Z-axis, but you'd still be subjecting it to axial loads when it does actually hit the material by doing it that way, and it would also be more complicated than just giving it a proper bearing setup which would be superior in every way.

edit - actually are you using a nema17 there? in that case it'll be more like 1kg-f axial load rating which would change the equation to being 5 times over load just hanging there.

double edit - I'm not sure why you think a steel framed build like this is innovative or indeed preferable to any of the other extrusion or wood based drawer slide builds? Indeed the only point I can see of doing a drawer slide build is that it's cheap and easy to build without access to any special equipment, which you kind of ruin the point of when you start talking about welding a steel frame. The components you are using don't have the accuracy or rigidity to benefit from the more sturdy steel frame, so it actually seems to be slightly defeating the point of these designs in the first place.

To me it seems like you're wasting what could be quite a nice little steel frame by then going and fitting it with sub-par components. assuming you've done a semi-decent job of alignment on that frame, if you took that same frame and fitted it out with some proper linear motion components (and stopped hoping that radial bearings could take thrust loads) you'd actually have a half decent machine there.

[Steel]

I just looked at the z axis on my 3020T and the lead screw is supported with one bearing on the top plate and either a bearing or sleeve on the bottom plate and the motor is connected with a flexi coupler so those bearings are being used to support axial loads even though there radial bearings. I cant see the difference by using the stepper bearings to replace that type of set up. Im using a 420oz nema 23 fitted with 6000z bearings.
I think i will make a stand to hold a nema 23 to replicate a z axis position with a 10kg weight mounted to a shaft hanging from the motor shaft to replicate what my setup and run the motor till the motor bearings fail !!
Again the point is to build this machine using using draw slides, I have a new set of 20mm supported rails with ball screws but i dont want to make a mid end machine. If it works great if it doesn't then ill make changes but for now ill do it how i wanted to do it and see how it turns out

[JAZZCNC]

I just looked at the z axis on my 3020T and the lead screw is supported with one bearing on the top plate and either a bearing or sleeve on the bottom plate and the motor is connected with a flexi coupler so those bearings are being used to support axial loads even though there radial bearings. I cant see the difference by using the stepper bearings to replace that type of set up.

And two wrongs don't make it right.!!

[njhussey]

please show me one youtube video of a fixed gantry draw slide build made of steel please, you wont find one !!!

Quick google brought this up.....found one



Question....if you've got decent linear components, why are you making this one?

[Zeeflyboy]

Fun video to skip through.

Look at how much the motor wobbles at 4:34 - that's a great example of what routercnc was saying about alignment causing extra load on the bearings!

[Steel]

Quick google brought this up.....found one



Question....if you've got decent linear components, why are you making this one?

Ok i was wrong there are a few out there after all

In answer to your question I saw one on youtube and thought to myself I want to make one of those and so here i am, Since i cant seem to sell my rails and ball screw kit maybe one day i will have the space and time to turn it into a decent machine but for now this build and my aluminum melting barbecue i put together on Saturday i should have enough to keep me busy in my free time.

[routercnc]

Yes, Nema 23 max axial load is 15 N. This means -

For Z stepper motor:
This has to react the Z axis parts which move up and down - if 3 kg then this is 30 N down
When plunging / drilling into wood this is typically 60 N up (giving 30 N in the other direction)
Drilling holes repeatedly takes the force from +60 N to -30 N which will work those bearings
Machining with helix cutters will also apply axial loads (due to the helix) - up to 20 N from memory

For X and Y stepper motors:
These have to react the horizontal cutting forces which for wood can be up to 50 N

All of these loads are well over 15 N so this is why everyone is recommending that the leadscrew has it's own bearings.

I seem to remember that steppers can have a bit of axial play in them, even when brand new. This means that there will be positional accuracy limitations. Angular contact bearing blocks on the ballscrew can be tightened up to remove this.

The final comment to make is that the leadscrews are usually not perfectly round, plus it would be difficult to align them perfectly with the axis of the motor shaft. This means there will be fluctuating forces being applied to the bearings each time the shaft rotates.

Finish the machine, run it for a month or so and report back how you get on, what worked, and what didn't.

References:
http://www.motioncontrolproducts.com...tors.php?cat=1
(max axial load)

http://ac.els-cdn.com/S1877705812021...5afb04f23aa36d
(drilling force in wood 4th page)

[Steel]

Yes, Nema 23 max axial load is 15 N. This means -

For Z stepper motor:
This has to react the Z axis parts which move up and down - if 3 kg then this is 30 N down
When plunging / drilling into wood this is typically 60 N up (giving 30 N in the other direction)
Drilling holes repeatedly takes the force from +60 N to -30 N which will work those bearings
Machining with helix cutters will also apply axial loads (due to the helix) - up to 20 N from memory

For X and Y stepper motors:
These have to react the horizontal cutting forces which for wood can be up to 50 N

All of these loads are well over 15 N so this is why everyone is recommending that the leadscrew has it's own bearings.

I seem to remember that steppers can have a bit of axial play in them, even when brand new. This means that there will be positional accuracy limitations. Angular contact bearing blocks on the ballscrew can be tightened up to remove this.

The final comment to make is that the leadscrews are usually not perfectly round, plus it would be difficult to align them perfectly with the axis of the motor shaft. This means there will be fluctuating forces being applied to the bearings each time the shaft rotates.

Finish the machine, run it for a month or so and report back how you get on, what worked, and what didn't.

References:
http://www.motioncontrolproducts.com...tors.php?cat=1
(max axial load)

http://ac.els-cdn.com/S1877705812021...5afb04f23aa36d
(drilling force in wood 4th page)

Thanks for the comments and info in the links

cheers Dave