Boring bar toolpost.

[thaiguzziParticipant @thaiguzzi]

That boring bar size looks fine.

I've done a couple of dozen HD Sportster 883-1200 conversions (thats 1/2" out of the bore!) on a roundhead Colchester Student, using a 1" diameter bar.

Just left two thou for the honing man at the engine recon shop.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 03/11/2019 13:53:21:

Assuming the rigidity and resistance to chatter is dependent on stiffness of the tool (a cylindrical beam).

[…]

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Also … please see my post at the bottom of p3 of the ‘Round Column Mill’ thread.

With boring bars; It’s not all about bending … torsional stiffness is also important.

MichaelG.

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https://www.model-engineer.co.uk/forums/postings.asp?th=143235&p=3

Edited By Michael Gilligan on 04/11/2019 07:37:40

[John MCParticipant @johnmc39344]

Posted by Lathejack on 03/11/2019 12:09:53:

The boring bar I have is 32mm. The bored out cylinders I've had in the past were upto 20 thou off centre, so not ideal. I'm certainly not risking my precious BSA cylinders being done the same way.

When you say off centre do you mean parallel error, up to 20 off centre but still parallel to the original bore. Or, the cylinder is leaning over? That is to say an error in perpendicularity.

As i said in my previous post, off centre error, a few thou is unimportant, perpendicularity is very important.

John

[HopperParticipant @hopper]

Posted by duncan webster on 04/11/2019 00:28:57:

If you get chatter on a long boring bar try winding lead or solder wire round it loosely. It rattles about and damps out the vibration.

That's a good trick. I've seen it done the other way too where long thin hydraulic ram cylinders off bulldozers etc were heavily wrapped with rubber strips cut from inner tubes while being rebored with some stupid long thin boring bars in lathes. Seemed to dampen the vibration and lessen chatter.

Twas something I saw done on a job in America. Those guys are not afraid to think outside the box to be sure.

Edited By Hopper on 04/11/2019 08:52:23

Edited By Hopper on 04/11/2019 08:53:33

[LathejackParticipant @lathejack]

Posted by John MC on 04/11/2019 08:02:27

When you say off centre do you mean parallel error, up to 20 off centre but still parallel to the original bore. Or, the cylinder is leaning over? That is to say an error in perpendicularity.

As i said in my previous post, off centre error, a few thou is unimportant, perpendicularity is very important.

John

Yes I know that a little off centre is not a problem, and that perpendicularly is important, you're right, and I agree. As I previously mentioned, the fixture ensures that the cylinders are bored square to the base mating face. But it also ensures the bore is on the original centre line, regardless of how important that is.

The bored off centre cylinders were square to the base, and appeared to have been running happily in that state. There's usually enough clearance between gudgeon pin bosses and the sides of the conrod little end for a little side to side offset, and a little front to back offset certainly won't matter, but there is no reason not to try and bore on the original centre line if possible.

The BSA cylinders are still on standard bore, but worn.

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