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Myford boring bar help

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Mark Gould 130/05/2019 22:06:31
222 forum posts
130 photos

Gents,

I recently bought a boring bar from Myford. It runs between centres and I was planning to bore the cylinder on our Stuart steam engine with it. It comes with some tiny cutters but I am not sure how it works. The bar itself has 2 holes drilled (both smooth, no threads in either) and these 2 holes are perpendicular to each other. The cutters fit very nicely in the holes with no discernable play but slide in and out without much effort.

My question is how are the cutters fixed in the bar?

Mark

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John Olsen30/05/2019 22:23:35
1240 forum posts
94 photos
1 articles

Usually the holes would intersect, and one of them would be tapped for a grubscrew. That is how it works on the ones I have inherited and made anyway.

John

ega30/05/2019 22:26:36
2486 forum posts
199 photos

Sounds defective but is there an axial push rod that secures the cutter?

David George 130/05/2019 22:54:36
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1807 forum posts
503 photos

Hi yes the cutter is clamped by a grub screw in the other hole which overlaps the cutter hole. You can set the cutter diameter by using a dial test indicator datum set on the boring bar and winding out the difference to set the bore diameter.

David

Andrew Johnston30/05/2019 23:25:59
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6574 forum posts
701 photos
Posted by David George 1 on 30/05/2019 22:54:36:

Hi yes the cutter is clamped by a grub screw in the other hole which overlaps the cutter hole.

That's what I thought, but the OP says that neither hole has a thread so could be a problem. May be a threaded version is extra!

Andrew

T.B31/05/2019 00:00:45
54 forum posts
21 photos

The 2 holes should just intersect each other .

One of those pieces of tool steel should then have a flat on the side.

This is used to act as a wedge against the cutting tool in the adjacent hole !

I have one the same and don't really like it as i find it difficult to adjust finely, its much easier to adjust and clamp with a couple of screws

Hopper31/05/2019 00:42:14
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6180 forum posts
319 photos
Posted by Mark Gould 1 on 30/05/2019 22:06:31:

Gents,

I recently bought a boring bar from Myford.

Best to contact Myford and ask. I've found them very helpful in the past.

Chris Trice31/05/2019 03:46:25
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1375 forum posts
10 photos

TB is right. I have one of these and one hole holds the cutter while the other has piece that is flatted on one side in a slight taper. The cutter is wedged in place quite firmly but adjustment is tricky.

Mark Gould 131/05/2019 09:05:45
222 forum posts
130 photos

Ok thanks for the replies. I will give it another look.

John Haine31/05/2019 09:35:14
4621 forum posts
273 photos

One of the ME books describes a gadget with a micrometer screw and presumably some sort of vee block that bears against the bar, so the screw can adjust the cutter by small amounts. Obviously applied between cuts. Can't remember where I saw it, Quorn book maybe?

ega31/05/2019 11:20:31
2486 forum posts
199 photos

Presumably, one of the OP's "cutters" was a wedge. An easy mistake to make and one easily avoided by the seller.

John Haine:

GHT gave instructions for a screw-adjustable boring bar which he intended for use on the Quorn castings.

Andrew Tinsley31/05/2019 11:34:51
1610 forum posts

Hello Mark,

It looks as if your boring bar is faulty, as others have said, do talk to Myford.

I don't like that type of boring bar, as I find it terribly difficult to adjust the tool accurately. I much prefer the type with a micrometer adjustment to set the tool protrusion. GHT gives a good design in his Workshop Manual. Another type is marketed by Hemingway Kits and doesn't take long to construct. In fact the kit makes up three boring bars of different diameters. If memory serves me correctly, the kit for three bars is about 50% more than the single bar from Myford.

I made up the Hemingway kit and was given a GHT boring bar as well! They are a joy to use, much easier than the Myford offering. Having said that, I am sure someone has found an easy way of adjusting tool protrusion on a simple between centres boring bar. It is just that I have not worked out how to do it!

Andrew.

roy entwistle31/05/2019 12:53:06
1504 forum posts

I'm sorry but I can't imagine why anybody with a lathe would buy a boring bar.

Roy

David Standing 131/05/2019 13:07:51
1297 forum posts
50 photos
Posted by roy entwistle on 31/05/2019 12:53:06:

I'm sorry but I can't imagine why anybody with a lathe would buy a boring bar.

Roy

If they do not possess a milling machine, perhaps to bore holes?

Seems a reasonable reason to me! wink

SillyOldDuffer31/05/2019 13:14:43
Moderator
8461 forum posts
1882 photos
Posted by roy entwistle on 31/05/2019 12:53:06:

I'm sorry but I can't imagine why anybody with a lathe would buy a boring bar.

Roy

A hefty boring bar turning between centres is unlikely to flex or chatter and it would do a good job boring a deep cylinder parallel. Never tried one myself but likely to be useful one day I think.

Always assumed the cutter was held by a grub-screw and doing it with a wedge is interesting. A home-made boring bar of that type would be very simple to make.

Dave

Edit: Whoops. I misunderstood what Roy meant!  They are easy to make if you own a lathe.  Sorry Roy.

Edited By SillyOldDuffer on 31/05/2019 13:16:34

David Standing 131/05/2019 13:18:24
1297 forum posts
50 photos
Posted by SillyOldDuffer on 31/05/2019 13:14:43:
Posted by roy entwistle on 31/05/2019 12:53:06:

I'm sorry but I can't imagine why anybody with a lathe would buy a boring bar.

Roy

A hefty boring bar turning between centres is unlikely to flex or chatter and it would do a good job boring a deep cylinder parallel. Never tried one myself but likely to be useful one day I think.

Always assumed the cutter was held by a grub-screw and doing it with a wedge is interesting. A home-made boring bar of that type would be very simple to make.

Dave

Edit: Whoops. I misunderstood what Roy meant! They are easy to make if you own a lathe. Sorry Roy.

Edited By SillyOldDuffer on 31/05/2019 13:16:34

Ah, don't worry, that's two of us misunderstood! blush

duncan webster31/05/2019 16:10:15
3919 forum posts
61 photos

I've got 2 of these, came with the lathe, but never used them. Looks like a right pain to get the tool at the correct radius and aligned correctly whilst you tap the cotter in, or does anyone have an easy way?

ega31/05/2019 17:43:33
2486 forum posts
199 photos

Is the wedge in fact a taper pin and does it project from the bar? If so, this seems another disadvantage to this design as it will constrain the projection of the cutter - the bit that matters!

Chris Trice01/06/2019 11:50:52
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1375 forum posts
10 photos
Posted by Andrew Tinsley on 31/05/2019 11:34:51:

Hello Mark,

It looks as if your boring bar is faulty, as others have said, do talk to Myford.

Andrew.

No, it is not faulty.

Andrew Tinsley01/06/2019 12:41:40
1610 forum posts

Hello Chris, thanks for pointing out that the bar is not faulty. I didn't realise that the cutter was secured by a wedge. That makes it even more difficult to adjust, unless you know of a good way. I would not give such a boring bar house room. The micrometer type is much, much better.

As an aside, I have a mill as well as a lathe. When boring cylinders. I much prefer to use the lathe and a between centres boring bar, providing that you can fit the cylinder on the cross slide. If the cylinder is too big to fit, I then use the mill as second best.

Andrew.

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