Boring bar toolpost.

Yes, but you also said that you wouldn't use that tool to bore the cylinder unless there were inserts suitable for Alluminium available for it. Which suggested that you thought it was going to bore out an Alluminium cylinder.

We still use these types of inserts on various cutters at work on Bronze, Alluminium, Cast Iron and various grades of Steel, with different grades of inserts still available.

Edited By Lathejack on 03/11/2019 19:34:55

While the propensity of a boring bar to chatter is related to the unsupported length it is less directly related to the deflection. Chatter is not caused by deflection, it is a cyclic change of deflection that causes the problem. It is counter-intuitive, but a way to kill chatter when boring can be to increase the depth of cut and/or increase the feedrate. This may increase the deflection, but makes the deflection stable; so no chatter.

Andrew

Didn't you read or understand my post? I said that inserts intended for aluminium are also very good for steel and CI (CAST IRON) using small depths of cut. Therefore putting less strain on the tool. Less strain means less flex on a tool which is having to bore a deep hole. Saving money by using the firms ancient tools is all well and good, but a compromise.

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 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.

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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

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

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

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.