Fitting a bronze bushing using a telescoping bore gauge

[WaltDizzy]

I recently fitted two bronze bushings into a the apron of a lathe. The openings are where the feed rod passes through the apron to drive the worm gear. Mine have a lot of wear. I used my milling machine to bore the holes, because I don't have a second lathe. Setting the gauge by levering it through the hole seems give me fairly repeatable results. However, I'm unable to find guidance on how the gauge is read with a micrometer.

One process that seemed to make sense was to find the minimum micrometer setting that would allow the set gauge to pass through its anvils with just a hint of drag. I used this on my first attempt, and the result was the bushing fit, but required a lot of force to drive completely home.

On my second attempt, I rotated the set gauge between the micrometer anvils and chose a micrometer setting that allowed the gauge to pass freely when in line with the anvils, but I could catch a tiny bit of drag if the gauge was rotated (like rolling a pencil) just right. This time the bushing went home with what seemed like a more reasonable amount of force. It also seems to mimic the motion used to set the gauge inside the bore.

For both bushings, which were quite thin walled, the inside diameter of the bushed hole collapsed by a tiny amount and I had to enlarge the hole to get it over the drive rod. The tighter fitting one required more material to be removed, of course.

Can anyone confirm that a telescoping gauge should be read as I've possibly re-discovered? I wouldn't rule out that I just got lucky that either one fit. This was my first attempt to fit a bronze bushing. It would be nice to confirm I'm using proper technique vs. being lucky.

 

[woodchucker]

your first is what I do, except I don't look for drag, just the slightest hint of it touching.. not necessarily drag... its a feel. if you tighten too much or look for drag, you may compress the points.

 

[GT-6 Racer]

These are tricky to get the feel of. It’s imperative that you are consistent with the starting angle in the bore. Make sure the screw is tight enough to take a good reading but not too tight. Again feel and consistency take practice. Mic the gage gently, as woodchucker says just a touch. I usually do 3 measurements before believing it when it’s critical. Practice with a known precision bore like a ring gage or a nice new bearing. You will get confident very quickly. The condition and quality of the gages are also quite important. Mitutoyo are nice. I only have a couple of them and 2 sets of Starrett which frankly aren’t as smooth but work well.

 

[ChazzC]

Although you see “old timers” holding the mic in one hand and the telescoping gauge in the other, I get better (= more consistent) results placing the mic in a stand.

 

[benmychree]

Sounds like you are on the right track, I agree with the others so far as feel is concerned, it just takes a bit of practice and years of sacrifice and self denial ----

 

[Bone Head]

Although you see “old timers” holding the mic in one hand and the telescoping gauge in the other, I get better (= more consistent) results placing the mic in a stand.

This is what I've used. Much better results.

 

[OTmachine]

Although you see “old timers” holding the mic in one hand and the telescoping gauge in the other, I get better (= more consistent) results placing the mic in a stand.

I use the stand setup for bore gauges. Telescope gauges, I adjust the mic until there is just a light touch between the anvils. Usually get within 2-3 tenths, as confirmed with bore gauge after several weeks of practice on the job. One of our guys was nicknamed “TT”, for two-tenths. Everything within two-tenths, as verified on CMM.

 

[projectnut]

I wouldn't be too concerned that the bushing "collapsed" slightly when installing it. Even off the shelf bushings are slightly oversize to be sure they fit tight in the bore. A typical 1/2" bushing (plain bearing) from McMaster has an OD of +.001" to -.000". Once the bushing is installed, it is typically reamed to size.

 

[mickri]

I use a stand made out of a magnetic base with a plastic clamp. Before I started using the mag base I held the clamp in a vise.



I found the biggest problem was learning how to take a consistent measurement of the bore with the telescoping gauge. Measuring the gauge with the micrometer was no big deal.

 

[homebrewed]

I will use a telescoping gauge until I start getting close to the target ID, then switch to a shop-made tapered plug. The final step(s) are trials with the bearing/bush itself.

I made an adjustable angle setter for my lathe compound so I can set it to a very shallow and known angle -- makes it easier to very finely advance the cutter into the work. 5.739 degrees gives you a 10:1 improvement. Since you don't have a lathe this option won't work, except perhaps to motivate you about getting some additional kit .