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Thread: Boring bar setting tool !
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16th May 2020, 09:15 PM #1
Boring bar setting tool !
Hi Guys,
As part of a discussion on another forum about line boring for miniature steam engine cylinders, I came up with this idea to enable a cutting bit on a boring bar to be adjusted accurately.
Boring Cutter Adjuster.png
Its basically a device that goes around the boring bar and pushes the tool bit forward. Using an M6 thread for the pusher will provide 40 thou or 1 mm per turn. Having index marks every 1.5 mm should make fractions of a thou relatively easy. As could adding a vernier scale.
Bugger, I've just spotted I've made an error in the knob calibration. It should be 39 not 49. Not to worry, it doesn't alter the way the device functions just the calibration.
I was calculating to get the index lines 1.5 mm apart to represent 1 thou ! That would make the knob diameter 19.01 mm, not 23.5 as I have shown. Or by making the index lines 2 mm apart would make the knob diameter of 25.46 mm.
The maximum boring bar diameter will be 20 mm down to about 6 mm.Best Regards:
Baron J.
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17th May 2020, 12:24 PM #2Golden Member
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Sounds like a good idea, I'm partway through a model engine and could have used something like that, I line bored the main bearings - a close fitting bush on the front and rear main bearings supported the boring bar, to set the radius of the cut I used the tool and cutter grinder to bring it to size, if though one doesn't have a T&G grinder then your idea looks good.
20190526_155339.jpg
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17th May 2020, 12:57 PM #3
Hi FamilyGuy,
Thanks for your post. That was the sort of thing being discussed. There were suggestions of using a micrometer to set the cutter which is what gave me the idea to use an M6 thread and calibrated knob.
Actually I hope someone checks my figures for the index and knob diameter, to make sure that I've got it right this time.
I think self isolation is addling my brain. Its 3 am here at the moment and I can't sleep !Best Regards:
Baron J.
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17th May 2020, 01:59 PM #4Most Valued Member
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I'm trying to get my head around how it's set up in the lathe?? Is it to wind out the cutting tool to the diameter?? Could you post some pics of it in action please??
Thanks.
KrynTo grow old is mandatory, growing up is optional.
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17th May 2020, 02:12 PM #5
Hi Kryn, Guys,
Thanks for your question.
The tool doesn't exist its just a drawing of an idea to do exactly what you think ! Yes the idea is that it is intended to push the cutting bit out in measured increments to arrive at the desired bore size. So you do need to be able to measure the bore. Then use the tool to push out the cutter to obtain the wanted amount of cut.
Usually the cutting bit is set in a drilled hole with a grub screw to secure it, loosening the grub screw to move the cutting bit often means that you loose the setting, with this tool you only need to loosen the grub screw enough for the tool to move it the required amount before tightening the grub screw back up.
At least that is the way its supposed to work. I will make one at some point and see.Best Regards:
Baron J.
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17th May 2020, 02:40 PM #6Most Valued Member
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Thanks for the explanation. Wouldn't it be just as easy to move the compound slide, or the cross feed slide??? Just thinking, as I'm basically a lazy person, why you'd spend time making a tool to do a job when something already exists on a lathe???
KrynTo grow old is mandatory, growing up is optional.
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17th May 2020, 05:56 PM #7Golden Member
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Hello Kryn
Have a look at the pic in post #2 if you look along the rod/boring bar that goes through the main bearings there is a small HSS cutting insert approx midposition, in practice the rod is turned between centres (ie between chuck and tailstock), the work is bolted to the cross slide and moves with the saddle as it is advanced towards the chuck, the rotating cutter bores the holes hopefully all in perfect alignment. The main bearings in the pic are around 12mm in diam, the rod/boring bar is around 8mm diam, I'm guessing I don't need to tell you how things would turn out if you tried to bore a 51/2 inch deep hole with an 8mm diam boring bar. It is a common way of doing things when making small engines, engine block in the pic is a 25cc V8.
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