Bearing journal finishing

What other methods do you use for finishing a bearing journal to size?

I need to finish a bearing journal to accept a bearing of 10mm bore....the finest feed rate on my lathe doesnt leave what I'd class as an acceptable finish plus there's the risk of taking too much off on a cut....

Grinding in situ is one way of finishing to size, but are there any alternatives to consider?

Lapping is a sure and steady way to bring a round to size with a good finish. I did this when I made a new mandrel for my little Flexispeed lathe.

Rod

Rod,

Could you elaborate a little on the lapping method please?

I guess the lap would have an internal bore finished to size? But how is the fine finish achieved on that?

Lapping paste, what is used as the 'wearing' material? Silicon carbide paste or something else?

Small block of MDF to support some fine Emery cloth will allow you to take those last few tenths off.

An external lap van be made by boring a hole off ctr through a bit of 1" thick brass say aboyt 1.5" dia. Slit the thick part and add a cross hole so you can close up the slot. Load with fine lapping paste and oil and run the lathe. There is one shown by Ramon in this post, worth reading the whole thread for all you need to know about lapping and honing model engines

Edited By JasonB on 03/05/2017 08:03:52

I used a lump of ally drilled to the nominal journal diameter and then split:

The lathe carrier screw can compress the lap as necessary as you proceed (a technique devised by Duplex many years ago).

I used 400 and then 600 SiC grit, sourced from the internet, mixed with a little light oil.

HTH,

Rod

You could make a poor mans external hone , by making a small vee block, and then using thin double sided tape or glue the fine wet and dry to it , or quite fine stones to it. Then us another sitting almost vertical above and polish away. For the 10mm bearing, if you want a press fit size for size . If you want a light slide fit, it is about 9.992mm and about 9.996 is a very light fit. Hope this helps, Fine is 240 to 320 paper or stones.

Neil

Combine Rod's [Duplex's] idea with Neil's and we could be on to a winner.

... The vee-block and opposing pad are almost there in the lathe carrier.

MichaelG.

Some good ideas, thanks chaps....

If the surface finish is not perfect, i.e it has tool marks on it, is the hone going to take them out or just polish the spots?

One more thing, if the lap is made from brass or aluminium, wont the grinding medium wear that rather than the work piece?

Edited By John Rudd on 03/05/2017 11:31:24

A hone or lap will remove the machine marks and give you a fine smooth finish. You can start with a coarser grit if the surface is rough.

The idea of using a softish metal for the lap is that the grit will embed in the lap and grind the harder metal of the job. It works very well and is a technique used with success by makers of i.c. engines which need a good surface finish for cylinders and pistons.

Rod

Depends too on the application. What type/material bearing are you going to use? What rpm and load?

Well thanks for the clarification.....

The application is for a gearbox shaft for an electric drill I'm refurbishing. The shaft has a 6000 ball race supporting it on the outboard end ( chuck end) while the inboard end is running in a bushing....Obviously the bushing journal needs to be pretty good in terms of surface finish, else it will rip the bushing surface to shreds.....rpm wise I think about 3000 revs, loadwise......ermmm well its a drill, so anyone's guess...

Hi John,

I don't know if you have read this: Laps and Lapping by Duplex. It gives you a good introduction and practical advice.

Thor

Glad I 'fessed up

Rod

Another fast-fingered poster misses out on a 'Tip of the Month' prize!

Neil

If you want to see how the professional does it, Robin Renzetti did a video on the subject. I suspect he's a couple of leagues above me but there are always things you can pick up....

Thanks Muzzer,

He under states the importance of holding parts if true roundness is required. The more round you want it, the harder it becomes. Having compounds that cut with little resistance is also understated in his video. The other secret with laps is that they are softer than the material being cut. The sunnen approach for external honing just can't be beat for roundness and the control of the taper. Lapping can take away material in areas that you do not need material removed. A high polish finish on a surface can be easily achieved with balsa wood and fine abrasives. Flexure laps for inside lapping have been around for a very long time and do work very well.

Honing allows you to get to the near very bottom of a hole or upto a shoulder on a shaft. Lapping often does not lend it's self well to blind holes and shafts with shoulders.

Neil

.

Really ?

For this application I would probably turn it to about one thou oversize, using a fine feed and light finishing cut, and then finish to size with wet rub paper and oil with the lathe running at about 1,000rpm. Quick touch with some coarser paper such as 400 or 800 grit then finish with some 1200 should do it.

Use small bits of emery paper that will not get caught up in the chuck and hold them lightly with your fingertips so they pull free if they do get caught up. Cover the lathe ways with a damp cloth or newspaper to keep the grit out of the ways and slides.