Xairflyer's first MDF CNC router

[Hobbiest]

Forstner bits have the bonus of making round holes as well, instead of the slightly oblong holes from a twist bit. Bearing blocks look great. What are the step sizes? 7/8" and 3/4?

[TopSpin80]

yea they are 7/8 and 3/4 the bearing isn't really tight in there, but there isn't much slop either.

Ernie

[Hobbiest]

should be tight enough once you get your washer on there. Another idea...use a fender washer that is just small enough to grip the outer race of the bearing, and drill two holes in the edge to mount it.

[ger21]

CMT makes 22mm forstner bits, for about $15. That is what those bearings are, right?

Gerry

[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?