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Myford Between Centres Boring Bar

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Simon Neath 225/02/2021 21:19:18
6 forum posts

Hi

I recently purchased the above but can't work out how to lock the tool to the bar.

The bar has two 1/4" holes at right angles to each other that just intersect but both holes are plain to take the tool bit. So how can I lock the tool in position what am I missing ?

Thanks

Simon

ian j25/02/2021 22:38:38
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301 forum posts
266 photos

Hi Simon.

It's a bit primitive really. The tool bit goes in one hole and is secured by a piece 1/4" diam bar with a flat tapering to the end on one side. Not sure if I have described it very clearly, if not I can take a photo of mine tomorrow.

ega25/02/2021 22:40:05
2053 forum posts
166 photos

The description is clear as far as it goes but one or two photos would help.

If this is a Myford bar then they should have the answer.

ian j25/02/2021 23:03:43
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301 forum posts
266 photos

Photo from Myford's Ebay listing.

myford boring bar.jpg

Simon Neath 225/02/2021 23:13:51
6 forum posts

Hi Ian

Thanks for your reply.

Hi Ega

I did ask Myford about a week ago but had no reply.

Simon

Simon Neath 225/02/2021 23:13:52
6 forum posts

Hi Ian

Thanks for your reply.

Hi Ega

I did ask Myford about a week ago but had no reply.

Simon

ega25/02/2021 23:33:49
2053 forum posts
166 photos

ian j:

As a cyclist, the solution should have occurred to me.

Presumably, the "cotter pin" has to be driven in radially and there is some risk of shifting the carefully adjusted cutter?

An alternative would be an axial screw-operated push rod.

Hopper26/02/2021 00:50:22
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5379 forum posts
129 photos

Looks like a pretty rubbish set up to me. As you say, the tool is likely to move when tightening the wedge. It is more common for the second hole to be threaded and contain a grubscrew to clamp the tool bit in position. But that hole is directly in line with the first for direct clamping force.

I made one to GH Thomas's design where the hole for the toolbit is at 45 degrees and a grub screw comes in at 90 degrees on one side. That way you can measure exactly with a micrometer how far the toolbit is sticking out of the bar because there is solid plain bar opposite the tool point to seat the micrometer anvil on.

But yours should be useable with the old time dodge of bore the hole the best you can then machine the piston or whatever to fit the hole size you ended up with. It may be possible too to adjust the tool bit by tapping on it with a hammer and drift without loosening the wedge so fine adjustment can be effected. Maybe. There must be some way they used these things in the wonderfully good old days and produced useable results.

John Haine26/02/2021 07:18:23
3777 forum posts
220 photos

At 1/4" you just about have enough meat to make a 2-part cotter pin with an axial screw. Get a bit of 1/4 s/s rod of length just less than the diameter of the bar. Drill to a suitable tapping size, then clearance to half the length. Locktite the piece of rod in the bar, and carefully drill through the tool bit hole (a 1/4 slot drill would be best) to form the cotter. Then remove with a little heat, cut the pin in half with a thin blade, and tap the smaller hole. This should allow you to clamp the cotter without moving the cutter and allow adjustment with a micrometer.

ega26/02/2021 11:46:41
2053 forum posts
166 photos

Here is an illustration from Bradley's Myford Series 7 Manual:

myfordboringbar.jpg

and some words of wisdom from ETW's 1951 ME Manual:

"In the simple type of cutter bar, the cutter is held by a grub screw or wedge, and radial adjustment is possible only by partial slackening off and tapping the cutter through. This is fairly satisfactory, except where a very close limit of dimensional accuracy is required; but in most cases where this method is employed, it is sufficient to machine the bore to as near the required size as possible, and fit any mating parts to it, such as cover spigots, piston, etc. Where high accuracy of bore size is important, however, it is possible to provide some means of fine adjustment to the cutter, though this is not so simple with small boring bars as with large ones."

Like Hopper, I made bars along the lines of GHT's design in which the cutter is not only screw-adjustable but directly restrained axially.

GHT was an exponent of the split cotter method put forward by John Haine but, apart from the limited "meat" available, there may be some advantage in grinding a flat on the cutter so that it maintains the same angle to the work after adjustment and gives a better chance of ending up with the bore to the desired size.

 

Edited By ega on 26/02/2021 11:48:10

Edited By ega on 26/02/2021 11:51:03

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