This may be in the wrong thread. If so apologises.

Plenty of MDF framed routers use pipe and skateboard bearings for the Z axis travel. This seems to work well.

Very few of the MDF framed constructors use linear bearings like these for their Z axis..
http://www.vxb.com/page/bearings/PROD/20mmLinearMotionSystems/kit995

Now, I can see that dust might be a problem without some means of preventing it getting in, unlike the skateboard way which is "self cleaning", but, apart from that, is there a reason for not using them?

I'm curious, and any opinions are very welcome,

Best wishes,

Martin

Alignment can be tricky, but I used them on mine, and although I haven't cut anything yet, they seem to work great.
http://www.cnczone.com/forums/attachment.php?attachmentid=13713&d=1136858794

http://www.cnczone.com/forums/attachment.php?attachmentid=13714&d=1136859518

Hi Martin,

I used them on a plywood machine for over a year and had no problems. The dust was taken care of by the wipers and I did not use lubricant. The only reason I stopped using them was because I built a bigger machine and used linear rails and blocks for more rigidity. To align them accurately I made a ply template and a hand router.

John

Dear Gerry.

I think your craftmenship is in a completely different league compared to mine!

I'm talking wonky drill-press, "bodge it with filler" stuff here. Maybe a bit better on a good day....

BTW, that is a great looking machine.

Thanks for the advice,


Best wishes,

Martin

Hi Martin,

I used them on a plywood machine for over a year and had no problems. The dust was taken care of by the wipers and I did not use lubricant. The only reason I stopped using them was because I built a bigger machine and used linear rails and blocks for more rigidity. To align them accurately I made a ply template and a hand router.

John

Dear John,

Thank-you for that.

I'm glad that I'm not alone in thinking of trying it on a timber/MDF gizmo.

Best wishes,

Martin

Dear Gerry.

I think your craftmenship is in a completely different league compared to mine!

I'm talking wonky drill-press, "bodge it with filler" stuff here. Maybe a bit better on a good day....


All the holes for the rails and bearings were drilled on a standard drill press. Double face tape the parts together and use a fence to keep everything aligned.

Dear Gerry,

Thanks for that. Could you tell me what the shaft spacing is? It looks about 6 1/2".

Best wishes

Martin

Dear Gerry,

Thanks for that. Could you tell me what the shaft spacing is? It looks about 6 1/2".

Best wishes

Martin

I can check tonight, but 6 1/2 is pretty close. If I recall correctly, the plates on top are about 8" wide.

I used them for all of the axis on my cnc router...

I would not recommend unsupported bearings on any axis greater than 12" And really a Z axis is ok because the load is usually static or within an very restricted amount of movenment.

So for the Z I give them a thumbs up... X&Y greater than 12" a big thumbs down unless you went with grossly large rails...

I used them for all of the axis on my cnc router...

I would not recommend unsupported bearings on any axis greater than 12" And really a Z axis is ok because the load is usually static or within an very restricted amount of movenment.

So for the Z I give them a thumbs up... X&Y greater than 12" a big thumbs down unless you went with grossly large rails...

Dear Nathan,

I was only thinking about using 20mm dia. shafts and linear bearings for the Z axis. The shafts might be about 15 inches long between their top and bottom mounting plates. The sliding carriage that would take the spindle might be about 8-10 inches tall , and the linear bearings themselves would, to a certain extent, reduce the tendency of the shafts to bend. I have not done the deflection calculations yet, but my guess is that the two shafts would not deflect by very much. I will check.

Best wishes

Martin

Dear Nathan,

Thanks.

Sorry for asking people more questions..

If you put a single 20mm dia. shaft, 15" long, on its side and put a 45 lb load at mid span, I think the deflection of the shaft would be about 0.3 thou inches. I'm not sure why I chose 45lb.

There are two shafts, and the spindle slide to some extent will reduce deflection because the linear bearings help keep the shaft straight. My guess is that the flexure of the MDF to which the shafts and spindle slide are mounted may be the weaker components.

I'm scratching my head about the actual forces involved. Common sense would suggest that the shafts do not have to take any great vertical loads as a column, but the bending loads will depend on cutter forces, and also the lever arm distance from the spindle to the shafts. Obviously it is a very good idea to keep the spindle to shaft distance as short as possible.

Has anybody got any idea what lateral cutter forces might be for non-aggressive cuts in MDF for a small Joe 2006 type machine? OK.. not a very well framed question... (and probably impossible to answer).

Best wishes

Martin

with 20 mm shaft i highly doubt you have anything to worry about ,
for the z on my last setup i had 1/2 ss stock and brass bushings that i made and it worked like a charm

with 20 mm shaft i highly doubt you have anything to worry about ,
for the z on my last setup i had 1/2 ss stock and brass bushings that i made and it worked like a charm

Dear dertsap,

Thanks for the encouragement.

BTW, the picture top left of your posts looks awfully like a certain "James" I last saw at the Isle of Wight Festival in about 1971. I could be mistaken.

As they used to say "If you can remember, you were not there"..

Best wishes

Martin

Dear dertsap,


BTW, the picture top left of your posts looks awfully like a certain "James" I last saw at the Isle of Wight Festival in about 1971. I could be mistaken.

As they used to say "If you can remember, you were not there"..

Best wishes

Martin
must have been something to see
unfortunately it was before my time to be able to live the true experience but then i suppose i did in my own way :)

Martin, my shafts are only about 4-5/8" apart (on center). They are 3/4", 18" long SS. It has 8" of travel, and is very solid.

must have been something to see
unfortunately it was before my time to be able to live the true experience but then i suppose i did in my own way :)

Dear dertsap,

OK you missed him, and the Doors, and a jaw-dropping gig from the Who who came on at 2-30 am lit by World War Two searchlights from a nearby hill.

"James" and the Doors are far better on recordings rather than live.

Feel no regret about missing them.

Best wishes

Martin

Martin, my shafts are only about 4-5/8" apart (on center). They are 3/4", 18" long SS. It has 8" of travel, and is very solid.

Dear Gerry,

Thanks for the shaft spacing and length information. Eight inches of travel sounds pretty useful too. BTW, and at risk of being even more of a pain in the ass by asking a lot of questions, what is the thickness of the uprights of your Y axis gantry? Sorry to keep asking...

Best wishes

Martin

The gantry sides are about 2" thick.

The gantry sides are about 2" thick.

Dear Gerry,

That's a good move. 1.5" seems a bit on the thin side to me, (and that is not any sort of criticism elsewhere).

Best wishes,

Martin

They're 2 layers of 5/8" MDF, with a 3/4" x 3/4" hardwood frame in between them, and a 1" square aluminum tube epoxied in rabbits running down from top to bottom.

Hi Martin,

I used them on a plywood machine for over a year and had no problems. The dust was taken care of by the wipers and I did not use lubricant. To align them accurately I made a ply template and a hand router.

John

Dear John and Gerry,

John You mention wipers. The bearings I have seem to have a hard rubber ring at each end. Are these wipers?.. or is something else needed.

Gerry Thanks for the encouragement. I did a trial with a jig fence and spacer. My wonky drill press tended to deflect towards the front as the forces from the Forstner bit (32mm dia") tilted the table out of right angle with the drill press column. I clamped a vertical strut down to the floor to support the front edge of the table and that improved things massively.
The sample bearing housings and shaft supports seem to be pretty good, and are in line. Anyway, it was obviously not a "bodge and filler evening"..

Best wishes to all,

Martin

Martin, here's a little more detail of what I did. Attach all the parts together with double face tape, and drill the smallest size hole you'll need (shaft size?) through them all. When you tape them together, use a fence to aligh them too so one edge is aligned on all of them. Keep that edge to the fence on your drill press.

Once the first holes are drilled, take the parts apart. For the parts that need larger holes, first, with the smal forstner bit still in the drill press, bring the bit down into the hole to align the part, and clamp it in place on the table. Then remove the bit and put the larger one in, and drill the hole without unclamping the part. That will keep everything aligned about as close as possible with the tools you have.

Mine actually has some very slight binding at the very bottom of the travel, but it's not nearly enough to cause any problems.

Dear Gerry,

Thanks for that.

I used a different method this evening.

I cut all the MDF pieces (a) bearing mount and (b) shaft mount pieces ( four in total) noting which edges and faces went against the saw fence, the saw table, and the cross-cut slide on my saw. Marked them too. The general idea being that they should be pretty identical when oriented in the same way on the drill press jig.

Drill press jig was just a piece of MDF with a small fence. I put in a stop, and used the shaft distance spacer to reference drilling centres from the first hole to the second. They were drilled individually for the simple reason that my drill does not have enough vertical travel to do otherwise. No chance to stack pieces, and anyway, my drill will wander if they could be stacked.

The strut on the front edge of my drill table was just to prevent sag from a mightly cheap machine bought about 17 years ago. The helical coil spindle return spring gave up about 4 years ago. Makes for interesting proceedures...

Anyway,

The shaft mounts were screwed to 18mm MDF and the bearing mounts to another. It actually seems to work really well.

Best wishes,

Martin

John You mention wipers. The bearings I have seem to have a hard rubber ring at each end. Are these wipers?.. or is something else needed.


Hi Martin,

Sorry I missed this post, for some reason I didn't get an email notification for a new post in this thread.

To answer your question if it’s not too late; yes the hard rubber rings are the wipers I was talking about.

BTW when I said I used no lubricant it is not strictly true, I gave the rails a wipe with WD40 from time to time.

John

Dear John,

Many thanks, and no, you are not too late.

Best wisges,

Martin

"wisges????

Martin