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Myford boring bar help

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duncan webster01/06/2019 14:20:03
3983 forum posts
65 photos

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 Trice01/06/2019 19:27:22
1375 forum posts
10 photos

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.

Ady119/09/2021 09:32:10
5089 forum posts
736 photos

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 Baron19/09/2021 09:43:01
520 forum posts
194 photos

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.

boring cutter adjuster.jpg

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.

Fowlers Fury19/09/2021 09:58:40
406 forum posts
91 photos

Reproduced - my posting here from 2018:-

The subject has been aired several times on here. After I made the simple version with vertical cutter, its shortcomings were soon evident. The main irritant being accurate measurement when advancing the tool tip. I then made one to the Geo. Thomas design and had no further problems.
(There were several postings on here in early November 2018 about b-c boring bars)
There are 2 sources of his design:-

1. GHT's original article in Model Engineer. Model Engineer, 3rd June 1977 p. 615 (Vol 143, No. 3562)

2. That most valuable compendium of GHT's articles - "The Model Engineers Workshop Manual (vol 1)" 1992. Pub: Tee Publishing, ISBN 1-85761-000-8. It's on page 92.

His comment about the normal, 90 deg tool resulting in flexure of a boring bar was well made IMHO. By putting the tool in the bar at an angle, that effect is very much reduced as well as resulting in very much easier ability to measure the swing with a micrometer. Geo. Thomas wrote “….the boring bar in its usual form leaves a lot to be desired. My main objection to it is the absence of any controlled means of advancing the cutter and all my design attempts to provide a suitable means ended in severe weakening of the bar at the point of maximum bending moment.”

IMHO it would time well spent to make one to the GHT design at the maximum diameter commensurate with your cylinder bores.

This was my GHT b-c bar boring out a 5" CI cylinder casting.


That brass item on the casting, under the boring bar, contains several small Neodymium magnets. It should have been within a plastic bag so that the collected iron bits could have been emptied straight in the bin !

not done it yet19/09/2021 10:17:27
6806 forum posts
20 photos

I would think that a cutter of less length than needing to stick out on the non-cutting side of the boring bar, and a threaded section to allow a fine pitched grub screw to advance the cutter, would be a good idea? Only a sensible solution for a decent sized boring bar, mind.

Russell Eberhardt19/09/2021 11:22:20
2736 forum posts
86 photos
Posted by Fowlers Fury on 19/09/2021 09:58:40:

I then made one to the Geo. Thomas design and had no further problems.

+1 for the GHT between centres boring bar. Not only easy to adjust but easy to measure the tool projection.


David Jenner02/10/2021 13:33:32
29 forum posts

Hemingway Kits do an interesting between centers bar, see link

Seems to address the adjustment issue.

Andrew Whale did a video on building them

Hope that is of some interest



Edited By David Jenner on 02/10/2021 13:34:01

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