Buy or make drill plates, stages or platforms to attach to linear bearing blocks?

[Goemon]

I was stupid enough to buy non-flanged bearing blocks for the THK rails for the long axis on my build. This means that, unlike the other axis, I can't use the actual bearing blocks as a jig to ensure precise hole positions for the mounting plates that go on top.

I partially got around this problem by using silicone mold putty and epoxy to make a copy of the bearing block surface to use as a jig. This works ok but, as I'm sure you guys know, if the position of the drilled and tapped holes are even a tiny bit off then the mounting screws don't fit, or get bent, or hinder the smooth motion of the axis.

The bottom line is that my drill press is not accurate enough to achieve the tolerances needed. The errors, while too small to detect with my eyes, are enough to cause issues. I have been making my mounting plates fit by drilling and tapping one hole to match the m4 threads on the bearing and drilling the second hole oversized to give me a little wiggle room. It works ok but it's not ideal.

How do you guys deal with tapped holes on mounting plates? Are you drilling and tapping precise holes and threads to match your bearings or are you using washers with oversized holes? Or am I the only idiot who bought bearing blocks with no flange?

I would have thought that THK or IKO would have sold pre-drilled mounting plates or "stages" to match their bearing blocks but I can't find any for sale as individual parts. I only see them on pre-made linear actuators like this:

https://www.ebay.com/itm/LINEAR-STAG...G8MJRWBarTIuxw

It would save a lot of time if you could just search for a mounting plate for an SR20 or SR15 bearing blocks....

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[ger21]

I don't understand what you are tapping? If your bearings have M4 threads, then you drill 5mm holes for your bolts, so that you have some wiggle room.
I also don't understand why flanged bearings would be any different?

[NIC 77]

The bottom line is that my drill press is not accurate enough to achieve the tolerances needed.

A tape measure, a square, a 0.5mm mechanical pencil, and a punch, that will get you close enough. The punch mark will help you align it when you use the drill press. Your drill press is accurate enough. Have you been using a punch and a sharp pencil?

How do you guys deal with tapped holes on mounting plates? Are you drilling and tapping precise holes and threads to match your bearings or are you using washers with oversized holes? Or am I the only idiot who bought bearing blocks with no flange?

To answer your question, on my current build I use my mini mill. It's not a CNC mill, but I use the hand cranks. I count the number of cranks, I figure it out ahead of time, and I manually remove the backlash before resetting the zero on direction reversals. My bearings mount to aluminum blocks. I also do the countersinking at that time. I use Socket head cap screws, countersunk, with washers and lock washers. The dimensions come out pretty much perfect doing it this way.

For things that are too large to fit in my vice on my mill, like some of the steel plate I am using, I used the method I already mentioned and it worked fine.

[Goemon]

I don't understand what you are tapping? If your bearings have M4 threads, then you drill 5mm holes for your bolts, so that you have some wiggle room.
I also don't understand why flanged bearings would be any different?

It seems like I was doing it (half) right without knowing it....

I was having trouble trying to drill and tap m4 screw holes in the mounting plates to attach to m4 threaded holes on the bearings. Even a 0.01mm variance in position or angle caused issues. If I use my M5 drill bit instead of the m4 one then my jig and drill press is accurate enough to make it fit properly.

I was assuming that the holes and threads had to be precisely match to the ones on the bearing blocks. I.e. I thought that the wiggle room might cause accuracy problems when in use.

Now I am really kicking myself for not asking you guys sooner.... I have been tearing my hair out trying to make those m4 holes line up perfectly... I would have finished my mounting plates weeks ago if I would have asked instead of assuming...

It was different on my flanged bearings because I used them as the jig. I have a set of those all-in-one drill bit and taps which allow you to drill and tap at the same time without moving anything on the drill press. I drilled directly through the holes on the bearing flange into the mounting plate which ensured a perfect fit and alignment of threads. It worked. Obviously, I can see that I didn't need to do that now but what is done is done.

[Jim Dawson]

Even the most expensive machine tools have the bearing block mount holes clearance size. Then the machine is aligned during assembly, once that is accomplished the bearing mount blocks are pinned to their mating parts. The more expensive machines are hand drilled and pinned with taper pins, the lower end machines use dowel pins, or even roll pins.

[Goemon]

A tape measure, a square, a 0.5mm mechanical pencil, and a punch, that will get you close enough. The punch mark will help you align it when you use the drill press. Your drill press is accurate enough. Have you been using a punch and a sharp pencil?



To answer your question, on my current build I use my mini mill. It's not a CNC mill, but I use the hand cranks. I count the number of cranks, I figure it out ahead of time, and I manually remove the backlash before resetting the zero on direction reversals. My bearings mount to aluminum blocks. I also do the countersinking at that time. I use Socket head cap screws, countersunk, with washers and lock washers. The dimensions come out pretty much perfect doing it this way.

For things that are too large to fit in my vice on my mill, like some of the steel plate I am using, I used the method I already mentioned and it worked fine.

I am aware of the various methods of marking the correct spot to drill and starting with a smaller drill bit etc. My issue was related to the backlash or shaft flex in my drill press given how little error it took to prevent a perfect fit.

Out of all the manual methods of creating jigs and premarking drill positions, using a cast replica of the bearing block with perfectly sized holes (for the drill bit) has been the most accurate for me. I.e. Using a jig like this:




Cast in low / no shrinkage resin from a quick mold made from silicone putty. It is a perfect copy of the original bearing block surface like this:



I have never been very good at precise measuring of the distance between hole centers and lining the drill up properly using pencil markings. Using a cast jig clamped in place is a lot easier for me. I know it is lined up correctly when the drill bit in the drill press goes through the hole in the jig.

It is an extra step though so I could see why more talented people would prefer to just measure, mark and drill.

[diycncmill]

I'm not sure if I'm getting your problem right but screwed parts are not aligned by the screws or exact hole positions.
You have to drill the plates so that you can fit in a screw without problems, no doubt, but you will have to bore a little bigger than the actual screw diameter is, for M4 I'd suggest to drill 4.5 or even 5mm holes.
Then you set the blocks on the plate and put the screws in but don't tighten them. Now align your block and the plate and only then tighten the screws and see if everything's still aligned.
Screws are not supposed to be stressed by shear but by tensile loading and therefore cause fricition on the screw-head which holds your parts together.

[...] are you using washers with oversized holes?

Yes, as mentioned above you always have to drill the holes bigger when working with threads.
I am always using washers when possible and on a possibly vibrating machine also spring washers so that screws stay tightened.

Best regards,
Dominik

[Goemon]

I'm not sure if I'm getting your problem right but screwed parts are not aligned by the screws or exact hole positions.
You have to drill the plates so that you can fit in a screw without problems, no doubt, but you will have to bore a little bigger than the actual screw diameter is, for M4 I'd suggest to drill 4.5 or even 5mm holes.
Then you set the blocks on the plate and put the screws in but don't tighten them. Now align your block and the plate and only then tighten the screws and see if everything's still aligned.
Screws are not supposed to be stressed by shear but by tensile loading and therefore cause fricition on the screw-head which holds your parts together.


Yes, as mentioned above you always have to drill the holes bigger when working with threads.
I am always using washers when possible and on a possibly vibrating machine also spring washers so that screws stay tightened.

Best regards,
Dominik

You might be right (about me not being right about the problem). This is not my area of expertise. Either way though, the solution that you and others here explained has made it all work for me. With slightly oversized holes or with one precise threaded hole plus one oversized hole it all fits like a glove.

The screws now go in and out without stress, bending or having the coating stripped off and the plate fit firm and flat with no perceivable play.

[diycncmill]

That sounds great!
Keep us posted on your further progress