Myford boring bar help

[Mark Gould 1Participant @markgould1]

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

[Mark Gould 1Participant @markgould1]

[John OlsenParticipant @johnolsen79199]

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

[egaParticipant @ega]

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

[David George 1Participant @davidgeorge1]

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 JohnstonParticipant @andrewjohnston13878]

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.BParticipant @t-b-2]

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

[HopperParticipant @hopper]

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 TriceParticipant @christrice43267]

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 1Participant @markgould1]

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

[John HaineParticipant @johnhaine32865]

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?

[egaParticipant @ega]

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 TinsleyParticipant @andrewtinsley63637]

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 entwistleParticipant @royentwistle24699]

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

Roy

[David Standing 1Participant @davidstanding1]

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!

[SillyOldDufferModerator @sillyoldduffer]

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 1Participant @davidstanding1]

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!

[duncan webster 1Participant @duncanwebster1]

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?

[egaParticipant @ega]

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 TriceParticipant @christrice43267]

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 TinsleyParticipant @andrewtinsley63637]

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.

[duncan webster 1Participant @duncanwebster1]

I do mine in the 4 jaw, bore and face one end, then machine the other faces using these 2 as datum. Won't work on piston valves of course. Fortunately my lathe bores parallel. Then finish off with a lap (or a hone if you know someone who has one the right size).

[Chris TriceParticipant @christrice43267]

I can't remember if it's Sparey or Mason but the practice employed for setting the Myford Boring bar is to use a micrometer set to measure half the required bore and half the boring bar shaft diameter. I've found it is possible to gently tap the wedge piece to let go of the cutter slightly, then tap the cutter to the right position before re-wedging it tightly. The measurement is taken from the cutting tip of the cutter to opposite side of the bar. Not the most convenient set up but inexpensive.

[Ady1Participant @ady1]

It sounds like a really good idea but you really need an adjustable setup jig to reliably change the cutting depth

Sounds like a Model Engineer Magazine project article for someone

[John BaronParticipant @johnbaron31275]

Hi Guys,

This is a drawing of mine ! I made it to specifically adjust the cutter. The nice thing is that once used its easy to set the cutter to increase the depth accurately.

It was designed for a upto 20 mm diameter boring bar. It works quite well on a smaller diameter bar as well. Otherwise just adjust dimensions to suit your bar.

[Author]

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