Between Centres Boring Bars

[GreensandsParticipant @greensands]

Hi – I have in my collection of tools a couple of between centres boring bars, one of 7/8" dia fitted with a 1/4" cutter the other 5/8" dia with a 3/16" cutter, the difference being that the larger bar with the tool set at an angle is fitted with a fine thread adjustment. In the case of the smaller bar the lack of such a feature is a distinct disadvantage and I have often wondered how things could be improved. One obvious thought is to tap out 2BA for a short length behind the tool but at a 90deg angle and a 5/8" dia bar there is not too much meat to play with. Are there perhaps other ways to include some sort of fine feed arrangement to take the hit and miss out of the equation. All suggestions would be most welcomed.

[GreensandsParticipant @greensands]

Fine Feed Adjustment for a Between Centres Boring Bar

[JasonBModerator @jasonb]

make an adjuster like these

[DC31kParticipant @dc31k]

The one Jason suggested is very nice.

If you search 'boring bar micrometer' and look at images, some of the results will give you some ideas. Any that include 'Van Norman' are not what you are looking for – it is the ones that look like a standard micrometer with the fixed anvil replaced with a vee block.

A vee-block with a micrometer barrel strapped perpendicular to the vertices of the two vees would work. Replace vee block with an old centre-square body and add micrometer.

Grind a notch in the cutting bit diametrically opposite the securing screw. Use a second screw with a tapered end engaging in the notch to advance the bit. Very limited range of movement with this though.

Use a normal micrometer across bit and bar after doing an initial cut and measure. If diameter of cutting bit is so large that micrometer anvil falls into the hole, use a gauge block to span the hole. This does mean you have to shorten the butt end of the cutting bit shown in the photo.

See also:

https://www.model-engineer.co.uk/forums/postings.asp?th=130528

https://bbs.homeshopmachinist.net/forum/general/37455-boring-bar#post721214

OK, found it. Search for Moore & Wright 462.

 

Edited By DC31k on 31/12/2020 10:38:52

[John PParticipant @johnp77052]

This combination of a boring bar and boring head works well ,with the cutter at half way along the bar .001 adjustment on the boring head = .0005 at the toolbit.. The normal boring tool fitted in the boring head is replaced with an articulated joint to connect to the boring bar ,you can just about see the Dore boring head and connector in this photo.

John

[DC31kParticipant @dc31k]

Posted by John Pace on 31/12/2020 10:37:26:

This combination of a boring bar and boring head works well

That is very good. Is the connector providing the drive in lieu of a dog?

I have seen boring heads used horizontally and stationary in the tailstock for taper turning (saves offsetting and resetting the tailstock).

I think the same arrangement would work for between centres boring (i.e. it does not matter which end of the bar the boring head is). Is that correct?

[egaParticipant @ega]

Greensands:

Your bars resemble those described by GHT in his ME Workshop Manual so I assume you have considered the excellent advice there?

[GreensandsParticipant @greensands]

Hi everyonel – Thanks for all the useful help provided. Had not thought of using a boring head in a between-centres application but can see how it could work. EGA, Yes I am pretty sure that the larger bar is a Geo Thomas design. Think my next step will now be to make up a Hemmingway type fine feed adjuster.

[John PParticipant @johnp77052]

Posted by DC31k 31/12/2020 10:49:04

That is very good. Is the connector providing the drive in lieu of a dog?

I have seen boring heads used horizontally and stationary in the tailstock for taper turning (saves offsetting
and resetting the tailstock).

I think the same arrangement would work for between centres boring (i.e. it does not matter which end of
the bar the boring head is). Is that correct?

Hi DC31k

The Dore boring head is made to fit on a Myford nose in the previous photo
this is mounted on an arbor held in the Warco chuck ,the boring head
provides the drive for the boring bar via the articulated joint is seen in this photo.
It is important that the joint in in line with the slides of the boring head,as the
boring head is adjusted the boring bar runs eccentrically to increase the cut depth.
The boring head can only be used at the headstock end and the tailstock
providing the support for the other end of the boring bar.
This was not my own idea but was seen in MEW issue 168
page 56 by Ted Barclay in which showed an amalgamation of a between
centres boring bar and boring head .

John

[egaParticipant @ega]

Posted by Greensands on 31/12/2020 16:06:33:

Hi everyonel – Thanks for all the useful help provided. Had not thought of using a boring head in a between-centres application but can see how it could work. EGA, Yes I am pretty sure that the larger bar is a Geo Thomas design. Think my next step will now be to make up a Hemmingway type fine feed adjuster.

More power to your elbow but can you not just mic across the cutter and bar as suggested by GHT?

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