tolerances

[pgk pgkParticipant @pgkpgk17461]

The bushing in my duplex cgnage gear was too tight..needed some severe persuasion to remove from the paired bearings in there. (Discussed with Chester before i attempted that in case of damaging the bearing since thisbush has a shoulder andthe inner race couldn't be protected. )

The bushing requires reversing when that duplex gear is reversed.

On to the question. The shouldered part is about 13mm long x 24mm diameterand was held in the 3-jaw. I indicated and best runout I managed was .2mm on the axle part of the bushing. (if I hadn't misread the DI I igh have tried longer to go to 1/100ths. The axle part is 1.5mm diameter and about 22mm long

Using the DRO I scratched and then fed in 0.02mm and took a slow shave. A test fit at that time was still too tight to push in by hand. I fed in another 0.005mm on the DRO shave again and hit it with some scotchbright.

It now slides in very easily.. acceptable but I'd have preferred it a tad tightter

Never having machined stuff to tolerance fits that seems odd. My first cut was a slow handwheel job because this feed gear was out…and anyway for a newbie this was close to the chuck. Is this a case of the cut raising a fine bur that should have been scotchbrighted before the second cut?

[pgk pgkParticipant @pgkpgk17461]

[pgk pgkParticipant @pgkpgk17461]

Correction. I hadn't misread the DI…(dumbo beginners!).. It was 0.02mm runout before machining.

[Michael GilliganParticipant @michaelgilligan61133]

pgk,

If I have read you correctly; a couple of points come to mind

1. You would probably have got the result you wanted by simply taking another coupe of passes at the same setting … to 'work the spring out of the tool'.
2. You do need very sharp tools to successfully take 0.005mm cuts.

MichaelG.

[pgk pgkParticipant @pgkpgk17461]

But the thing ended up too thin. Surely spring passes are there to effectively 'get it thinner to size'.

This was also a 12mm tool bit ground for facing that hadn't done more than a few inches of surface distance since ground and honed and here was being used on the ack edge of it's radius 'cos I'd angled it to get into the shoulder. While I'm new at tool grinding the cutting edge used was effectively new. The swarf was bum-fluff anyway on such thin passes.

Unless it dug iself in a tad on the 0.005mm?

[Nick_GParticipant @nick_g]

.

0.005mm is close to 1/10th of a thou in imperial.

That is a big ask for most lathes and a large portion of measuring equipment that the avarage home user is likely to use unless he has very deep pockets.

A DRO at those close tolerances would have to also be serious money and calibrated by a specialist once installed on the particular machine. Even then temperature variations in the workshop could easily throw a spanner in the works unless it's taken into consideration.

Nick

[Tony Pratt 1Participant @tonypratt1]

Posted by pgk pgk on 07/01/2015 18:55:33:

But the thing ended up too thin. Surely spring passes are there to effectively 'get it thinner to size'.

This was also a 12mm tool bit ground for facing that hadn't done more than a few inches of surface distance since ground and honed and here was being used on the ack edge of it's radius 'cos I'd angled it to get into the shoulder. While I'm new at tool grinding the cutting edge used was effectively new. The swarf was bum-fluff anyway on such thin passes.

Unless it dug iself in a tad on the 0.005mm?

I guess Michael is saying it would have been wise to take a couple of cuts without moving your slide in by .005mm, that procedure may have been enough to get a better fit or maybe not? In reality .005mm movement on a lathe slide is a big ask.

Tony

[pgk pgkParticipant @pgkpgk17461]

Ah! That makes sense.. thanks.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Tony Pratt 1 on 07/01/2015 19:22:10:

I guess Michael is saying it would have been wise to take a couple of cuts without moving your slide in by .005mm, that procedure may have been enough to get a better fit or maybe not? In reality .005mm movement on a lathe slide is a big ask.

.

Exactly that … Thanks, Tony

MichaelG.

[pgk pgkParticipant @pgkpgk17461]

Points well made, chaps. There's a lot for a newbie to learn and remember. Perhaps next time I'll dig out my honing paste and leather wheel as well

[Ian S CParticipant @iansc]

Perhaps instead of a lathe tool, a strip of fine wet & dry paper, backed with a 6" steel rule, and just polish the .005 mm.

Ian S C

[Author]

Posts