Xairflyer's first MDF CNC router

[TopSpin80]

Looking at theses things I don't really think anything needs to be done to them as far as the tightness. I do need a drilly press though, to make the holes straighter. I had a freind that had a small mill he wanted to sell. If I can find his number and he still has it I'm gonna buy it.

[xairflyer]

I have been looking through various posts, on lead screw (drive screw) fitting and I can't seem to figure out why a thrust bearing arangement is used for the end of the thread.

I was going to mount a rod end type moveble bearing (to allow for any miss-alignments) to the end plates and just stick the threaded rod (5/16") through it.

Can anybody explain what I am missing, or not considering ?

[Stevenpats]

The thrust bearings keep your leadscrew from moving back and forth when it accelerates or decelerates against the table load. I use 1/2"-13 threaded rod and 1" delrin nut for drive. The rod is turned down on my lathe to the ID of the thrust bearings,and sandwiched, I did not use a tensioning arrangement. Tensioning the leadscrew would have helped a bit with whip, I get a bit with rapids, when the table is at far travel. I did leave about 3/4" of excess rod out the end of thrust bearing, enough to thread with a die for a tensioning nut/washer arrangement if I feels its needed.
Steven

[Hobbiest]

I hear mcmasster-carr has thrust bearings with 3/8" ID and a flange on one end. Haven't checked it out yet but they prolly do. May even have different sizes.

[xairflyer]

Got the X axis/table all setup last night. Takes a bit of time to get everything right.

I first got the base of my machine on it's stand perfectly level in all axis, then set the table in and got the rails parallel (ish) so that the table ran freely with the side bearings touching at all places.

I then removed the table and leveled each rail fore and aft, then from one rail to the other, and back & forward, and back & forward as each adjustment effected the other.

I the checked the parrallel'ism with a large verner, then back to the level of the rails again !!
Eventually I got it that I was fairly happy.

Re fitted the table and checked it for level on the rails. Only one bearing was out, a bit too low, which caused the opposite bearing to sit above the rail i.e. not touching.
Looks like it was worth while spending the time marking out the bearing positions on the angles very accuratly.

Turned up an insert out of nylon to fit the ends of the tubes, just to stop the adjusting bolts from disforming the tube. Not that the stainless pipe I used would be easy to squeeze, but I though it would look better too.

[Mr.Chips]

Just a word of caution.
MDF is very dense but it doesn’t have very much linear strength to support it’s self and will sag and flex very easily over relative short distances. Neat looking table just be sure you have a couple of supports under the machine to keep the base plate flat.
I’m building a movable machine also and the table is 24” wide. When I installed it, it was flat, but just over a few days it has started to sag just under it’s own weight. Mea by it’s the humidity here?
I found a used piece of 1” delrin and will replace my table with it. Before I found the delrin I was thinking about adding some kind of metal brace for added rigidity.

Torsion Box
http://www.diynet.com/diy/shows_wwk/..._26946,00.html
Another way to eliminate the sag would be to make a torsion box type table. But this would make the table thicker.
Anyway it’s a thought.
Hager

[balsaman]

AirX,

Slot the hole in the alum. angle so you adjust the offending bearing and retighten.

E-man

[Hobbiest]

Don't know about \delin, but UHMW is similar and flexes and contracts readily with changes in temp. Why not get a cheap piece of aluminum angle and cut into pieces to reinforce?

[Hobbiest]

Thatdelrin is probably as expensive as aluminum plate .25!

[xairflyer]

Don't think I will have any sag problems, the MDF is 1" thick and it is sitting on a frame of 2"x1" steel box section with a support every 9".

Balsaman that's what I done to adjust the bearing.

[Mr.Chips]

The Delrin was free. It is 1" thick and has lots of 1/4" holes, it was to be a vacuum table in a lab but they made a mistake during machining and it was trashed.

Nothing to loose, had only to cut 1" off the width for it to fit my table. And I could not make it flex.

Xairflyer,
You wont get any MDF flex on that table.

Hager

[Hobbiest]

Ok, so the delrin will be on top of the MDF? What I was talking about was unsupported lengths of plastics warping like crazy, but if it has an MDF backbone that it is screwed to it should be fine. But why use the delrin if in fact you are keeping the MDF too?

[Mr.Chips]

Sorry I didn't make myself clear. I removed the MDF table and replaced it with a piece of delrin that was 1" thick.

Are you sure this material will "warp like crazy"?

It is really rigid, I could not make it flex any by placing one end on the floor and the other end on a 2X4 and standing on it. 210Lb. The 3/4" MDF could be flexed by pressing on it, without standing on it.

I'll try it and if it doesnt work out, I'll cut it up and make antibacklash nuts out of it. Can get alot out of a piece that is 1" X 24" X 30" even cutting around the holes.
Hager

[Hobbiest]

But then you would have to build more machines! Like I said, I don't know about delrin specifically, but UHMW which is similar is very thermal sensitive in large pieces. Anything more than about 3/4", and it swells and contracts. I have a 2" by 3" by 3ft piece, and it is very solid, yet always has a different profile! Anyway...just my two cents.

[gmfoster]

I don't know if Delron warps ut UHMW sure does.



Garry

[xairflyer]

Have the x axis motor fitted and the table moving under it's own steam !!

Tricky job to get the Delrin nut/plate fitted under the table.

I first screwed a 1" x 2" x 5" block to the bottom of the table in the middle. I had already worked out that the lead screw would be approx 1" below thw table so I drilled a 13mm (1/2") clearance hole to allow for any slight misalignments.

I made a delrin plate (no antibacklash for now) and pre drilled two holes in opposite corners for screwing to the support block.
Screwed on the delrin nut, and refitted the table.

Screwed up the plate until it came in contact with the support block, and very difficultly (as there is only 2 1/2" under the table) managed to clamp the delrin plate to the support block.
I then removed the screws holding the block to the table from above and lifted the table out of the way.

All I had to do then was unscrew the threaded rod and drill my holes.
A tricky job, but it was worth it as everything runs nice and true.

I rigged up my test driver board and I am not getting much speed, with a 3.9v 1.35A motor running on 12v with two 6R8 res (6 wire) turning a 8mm (18tpi) screw, the best I get is 10" min.

How can this be increased, I was thinking of changing to 10mm or 12mm all thread ?

Will a larger 2A, 3.6v, 127ozins torque motor go any faster ?

[xairflyer]

Does anyone know how to attach more than one picture in each meassage ??


Started fitting my Y axis

[cncadmin]

Originally posted by xairflyer
Does anyone know how to attach more than one picture in each meassage ??

This site can't do that right now but the new one will.

[balsaman]

Need more voltage for more speed. What driver board are you using? 10-12" is normal for a 12 volt supply.

Eric

[Hobbiest]

check out Steve Manzer's site here, he is getting double that speed with 20tpi rod.
http://www.angelfire.com/ego/stevenm...CMachines.html