Boring Bar Setting Device

I am hoping to be doing some boring between centers on my next engine to achieve a long true bore for the cylinder. A friend and fellow model engineer helpfully showed me a picture of a device had had made to measure reach of the cutter from the boring bar. This is only part one and I hope to finish it shortly, it has taken much much longer than expected, probably because my efforts working on the bar have been split into lots of little spells in the workshop… anyway, hopefully finish tomorrow evening. The plans for this device are in a back edition of model engineer.

A piece of scrap ally I rescued months ago!

The main 2 pieces cut to shape with the guide rods. I deviated from the plans here which stated to bore 1/4″ and loctite the guide rods into the top T shaped piece. I didn`t fancy that, so I decided to only drill 2/3 of the way through the top piece and thread the top of the guide and screw it in position. Will probably use some thread lock on final assembly. I`m pleased with this, it looks tidy (not drilled through) and certainly solid. It also can be disassembled should it need to be.

This sort of shows how it will work. The two V slots will clamp down onto the boring bar with them bolted together using the guide bars. I now need to make a plate on the top which will hold a DTI and a plate on the bottom which will hold the adjusting screw.

Hopefully it will be obvious how it is used once complete!

I finally completed the boring bar setting device after many more hours than expected.

Here are all the parts required. I have used stock M3 screws for the supporting brackets and a stock M4 screw for the grub screw to hold the dial in place.

The plans also required that a flat button is made for the DTI in use so that you can measure the maximum projection of the boring bar

Initial mock setup on a piece of ally bar. I`ll be using a steel bar for the boring bar when I get around to cutting it. It works by turning the screw at the bottom which will push the tool steel through the boring bar and the DTI will measure the distance and therefore the bore radius.

And a final assembly

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3 responses to “Boring Bar Setting Device”

  1. Benji D says:

    Hi Raynerd
    Good website, I`ve learn a lot. Plenty of interesting articles and good clear pictures. However, this has stumped me, I just don`t get what it is. Could you explain?

    Benji D

  2. DavoDavo says:

    Benji, I think it works like this:
    Imagine you want to bore a hole through a casting that already has a smaller hole in it. The casting is held on the cross-slide in the appropriate position. The steel boring bar goes through the casting and is supported between centres so that it is aligned with the lathe axis.

    The boring bar has a square hole in it, to take a piece of square tool steel, at right angles to the lathe axis. The boring bar will rotate by using a lathe dog at the chuck end.

    The Boring Bar Setting Device allows you to move the piece of tool steel that is in the square hole by means of the screw (the back of the tool must protrude out of the boring bar for the screw to contact it).

    You turn the screw until the cutting tool tip is moved outwards – depressing the dial gauge plunger as it does so.

    You will have previously measured the diameter of the boring bar (say 20mm) so take half that measurement (10mm) and add it to the amount of travel of the indicator plunger after it was first set flat against the boring bar. As you screw the tool outwards you make the cutting radius larger.

    So, if the boring bar is 10mm radius and you have moved the tool 5mm out (as measured by the dial gauge) from the boring bar itself then it will bore a hole that is 30mm diameter when you move the carriage along.

    Hope that helps.
    Cheers, Dave.

  3. Raynerd says:

    Would it be OK to copy that (giving you full credit) into the main page info??

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