[RomanLini]

As a suggestion you could use a slippery plastic like a PE or Delrin. If you drill the 1/2" hole in a small (1/2" thick, 3" square?) piece of the plastic at can act as the bearing. Then the plastic screws to the aluminium plate, which also allows some alignment there.

[ToshiroTamigi]

Have you verified that with that kind of joints the acme won't move?
Doesn't that joints acts like a spring if you pull or push the acme screw?
I think you may put some sort of axial bearing (any ball bearing will do the job given the limited force applied) at the end of the screw (the one without motor) and a collar to eliminate any possible screw axial motion.

[fuper]

As a suggestion you could use a slippery plastic like a PE or Delrin. If you drill the 1/2" hole in a small (1/2" thick, 3" square?) piece of the plastic at can act as the bearing. Then the plastic screws to the aluminium plate, which also allows some alignment there.

Really good idea RomanLini!

I will use this approach if I encounter any problems. I like the ability to make adjustments.

[fuper]

Have you verified that with that kind of joints the acme won't move?
Doesn't that joints acts like a spring if you pull or push the acme screw?
I think you may put some sort of axial bearing (any ball bearing will do the job given the limited force applied) at the end of the screw (the one without motor) and a collar to eliminate any possible screw axial motion.

You might be right. I've never used them before so I am not sure what to expect. They are for shaft mis-alignment and they are springy. However if you turn them radially they are very stiff, I cannot move them by twisting either end by hand.

[fuper]

How does one make the title/subject Red like other build threads?

[RomanLini]

When you first started the thread there was as option box you could select to tag it as a "build thread". I'm not sure if you can change that now, probably not. The moderators might know some way to do it.

Nice photo too, it's starting to look like a machine.

[fuper]

When you first started the thread there was as option box you could select to tag it as a "build thread". I'm not sure if you can change that now, probably not. The moderators might know some way to do it.

Nice photo too, it's starting to look like a machine.

Well if a Moderator would be so kind to toggle that, it would be nice!

Thanks for the kind words about the machine. I'm waiting on orders at this point, shafts, linear bushings and the stepper driver.

I still have to design the Z axis, not sure how I will do that yet. Thinking about just getting the other two axis up and running then tackle the final one. I'm a little concerned about weight although if I understand things correctly, the mechanical advantage given by a screw is:

MA = (pi * screw-diameter ) / lead-of-screw

I'm not sure what the lead of screw thread is for my 1/2-10 rods, just guessing I would say .1 [10 threads per inch]

So MA = ( pi * .5 ) / .1 = 15.71, rounded up

160 oz/in steppers => 2513 oz/in

This probably wrong

[RomanLini]

That's not bad. The mechanical advantage is given from the driving circumference, over the driven distance. Your driving circumference is a little less than 0.5" say 0.45" average, and you need to de-rate a lot for the friction (reduced drive efficiency). Also you need to de-rate for load forces and higher stepper speeds which have less torque.

I would say;
0.45*Pi/0.1 = 14.13 (perfect model)
then de-rate 50% for your leadnut friction and 50% for reduced motor torque;
14.13 * 0.5 * 0.5 = 3.53
So that's 160oz*3.5 = 560 oz force

If your leadnuts are some "tight" design like plastic nuts on the metal screw it might need derating some more, likewise if you have any bind on the moving parts, linear bearings etc.

Re the Z axis it helps to finalise most of the Z design as that will determine where the cutting tool bit is, and that determines where you need to have the moving table to get full cutting area.

[fuper]

Drat!

For some reason I thought I purchased 12mm linear bushings. Instead I got 16mm. I put an order in already for 4 x 13" 16mm hardened rods from vxb.com

Let me know if anyone wants em.

[fuper]

That's not bad. The mechanical advantage is given from the driving circumference, over the driven distance. Your driving circumference is a little less than 0.5" say 0.45" average, and you need to de-rate a lot for the friction (reduced drive efficiency). Also you need to de-rate for load forces and higher stepper speeds which have less torque.

I would say;
0.45*Pi/0.1 = 14.13 (perfect model)
then de-rate 50% for your leadnut friction and 50% for reduced motor torque;
14.13 * 0.5 * 0.5 = 3.53
So that's 160oz*3.5 = 560 oz force

If your leadnuts are some "tight" design like plastic nuts on the metal screw it might need derating some more, likewise if you have any bind on the moving parts, linear bearings etc.

Re the Z axis it helps to finalise most of the Z design as that will determine where the cutting tool bit is, and that determines where you need to have the moving table to get full cutting area.

Ah I didn't think about "ideal" vs "actual". A reduction like you described is totally right. Still 500+ oz/in is pretty nice. I feel that many people don't consider the mechanical advantage when they purchase stepper motors.


Shane

[fuper]

Each pair of posts has a linear shaft between them. The shaft size is 16mm which is a hair near 5/8"

I've tried drilling in a drill press with a 3/8 then slowly [slowly!] bore out the rest with a boring head attachment for my Taig Mill.

Thing is I'm not that good [likely] or boring on a benchtop mill is not that great [somewhat likely].

I always get the hole a little over the correct size so the shaft wobbles!

I'm thinking that this may not matter. I could simply drill and tap a set screw to tighten the shaft down. I suspect I might have to shim the posts themselves for a perfect alignment.

Should I shim the hole somehow? Not sure.

[RomanLini]

What I would suggest is to clamp the shafts in alignment plates. Similar to what i suggested for the bearing plate for the free end of the leadscrew. If you get a bit of plate say 3" square, and make a hole that clamps the 16mm bearing shaft tight, that 3" plate can then be bolted to your upright plate with 4 bolts.

You can use a screw to clamp the shaft in the 3" square plate, or maybe a clamp screw in a slot to clamp it all the way around.

The benefits of that system is that you can clamp the shafts secure then still have the ability to align both ends of the shafts (as the 4 small bolts have loose holes for adjustment).

Since you are hand cutting and drilling everything it will be handy to have the ability to align and adjust everything.

[hazardouschurch]

Nice build i got to ask how much did you pay for the aluminum? Im building mine out of steel because i have a moderate shop with a welder but i dont have a mill T_T. Originally was thinking of using aluminum but decided to go with steel and payed 25$ for all the tubing for my 2'X4' machine. Have not finished it yet but already thinking of making another smaller cnc for pcb and aluminum work. It would be cool if you posted what you have payed and then the total at the end would make incentive to use your plans.
Thanks
Hazard

[fuper]

What I would suggest is to clamp the shafts in alignment plates. Similar to what i suggested for the bearing plate for the free end of the leadscrew. If you get a bit of plate say 3" square, and make a hole that clamps the 16mm bearing shaft tight, that 3" plate can then be bolted to your upright plate with 4 bolts.

You can use a screw to clamp the shaft in the 3" square plate, or maybe a clamp screw in a slot to clamp it all the way around.

The benefits of that system is that you can clamp the shafts secure then still have the ability to align both ends of the shafts (as the 4 small bolts have loose holes for adjustment).

Since you are hand cutting and drilling everything it will be handy to have the ability to align and adjust everything.

Thanks for the continued feedback and suggestions. I experimented drilling several holes and boring to size last night and didn't get the results. I will be going with your suggestion.

I've got .5" flat bar I'll cut to size, measure and drill out 4 holes slightly oversized. I can tap it into alignment.

Thanks!

[fuper]

Nice build i got to ask how much did you pay for the aluminum? Im building mine out of steel because i have a moderate shop with a welder but i dont have a mill T_T. Originally was thinking of using aluminum but decided to go with steel and payed 25$ for all the tubing for my 2'X4' machine. Have not finished it yet but already thinking of making another smaller cnc for pcb and aluminum work. It would be cool if you posted what you have payed and then the total at the end would make incentive to use your plans.
Thanks
Hazard

Thanks for the kind words. Your suggestion is a good one! I will certainly post the prices when everything is complete, until then:

I paid $35 for the MIC-6 plate.
I paid $22 for the extruded aluminum 1/2" x 2 1/2" x 48"

I needed more than 48" so I purchased two.

So around $79 in material.

I paid $33 for 4 Lin Engineering Unipolar Steppers.
I paid $49 for 2 x 36" 1/2-10 acme rod + 7 nuts and flanges
I paid $34 for 4 16 mm linear bushings.
I paid $40 for the 16mm x 60" linear rod

So around $156 in hardware

I purchased everything except the linear rod from Ebay. The linear rod I found on ebay but the seller's store outside of ebay was cheaper.

[fuper]

Well I got my first order for the Millbox directly from China. I couldn’t find a US source for a reasonable price, and the price range I was looking at they all seem to be by the same manufacturer in China.

They fit nicely on the 2.5″ aluminum stock I’m using for the build. Being metric the holes are M5. You will have to accommodate for your design as you should use whatever part you can source cheaply and inexpensively.

These blocks appear to be cut from an aluminum extrusion. The 4 mounting holes are drilled and tapped and the ball bearing bushing inside is held with two retaining rings on either side. I’m not sure how accurate they will be yet. If they are not that great I’ll switch to a slippery plastic like Delrin [thanks RomanLini!] and just have it bored for me at a local machine shop.

[DSpeck]

If you are still having troubles getting the holes the right size, you could try drilling them about .020-.030" undersized, and then reaming to final diameter. This should give you a very close fit, and if you are worried about runout, try using a reamer that is .001"-.002" undersize, which should give you a tight fit.

If you do this method, I suggest you clamp or bolt all 4 corner blanks together, then drill/ream them all at once, so that they must all be the same height from the table.

[hazardouschurch]

Are you going to put bearings on the end of the linear screws. Should help with the life of the screws.

[fuper]

If you are still having troubles getting the holes the right size, you could try drilling them about .020-.030" undersized, and then reaming to final diameter. This should give you a very close fit, and if you are worried about runout, try using a reamer that is .001"-.002" undersize, which should give you a tight fit.

If you do this method, I suggest you clamp or bolt all 4 corner blanks together, then drill/ream them all at once, so that they must all be the same height from the table.

Thanks for the suggestion Dspeck! I've considered this, and might try this out! Right now i'm starting out so I don't have a lot of tools so I've hesitant to purchase reamers for a 16mm size.

My drill press is just a standard 10" craftsman from sears and I'm not that impressed with its accuracy so far. My mill only goes up to 3/8" for the drill chuck making it hard to find right sized screw machine bits.

I will likely just go ask kindly for a local machine shop to bore out whatever I end up going with, I figure once i explain what I am doing they won't charge that much [hopeful!]

Shane

[fuper]

Are you going to put bearings on the end of the linear screws. Should help with the life of the screws.

Hi Hazardouschurch,

A few others have brought up this issue. I will likely go with delrin end plates that support and bolt on the end of the post. Thanks for pointing this out!

Shane