Gallery, Projects and General > How do I??

Drilling around the circumference without RT

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raynerd:
Hi, I was wondering if anyone could lend me some advice regarding drilling holes around the circumference of a bar without a RT.

I have a 1.5" bar and I wish to accurately drill three holes along 1" circumference at 120deg divisions. Clearly this would not be a problem with a RT or dividing head but I don`t have either and I am not in a position at this moment to purchase one.

My plan would be to accurately scribe the desired circumference using a fine point tool in the lathe, pop a hole somewhere along the circumference and then simply get a pair of dividers and trial and error move them from the point in two steps along the circumference until they return exactly back to the spot. Once I have got the desired position - mark and pop the remaining two points.

Alternatively there is a method of setting up a jig but my concern there is that the holes will only be as accurate as the jig and therefore in my opinion there would be less error in marking the divisions directly onto the work?

Any advice appreciated - I know a RT would be ideal but I`m sure there must be methods of doing this accurately without?

Chris

Darren:
Have you got any hex bar?

raynerd:
I do - I have quite a large brass or bronze hex bar that is about 1" across and I`ve never cut into (picked it up from the scrap about a month ago) and then some much smaller ally that I picked up yesterday. What are you thinking ....?

Chris

Darren:
Hex has six sides, use every other two and you have your 120deg.....

I'm sure you can think of a way of using that info.... :thumbup:

raynerd:
Now that is food for thought!  :smart: It is a pitty - I`ve just spent £20 on materials but I could have used hex, marked and drilled and then turned it down to round. Perhaps I could use the hex I have as a jig - then I know the holes or marking on the jig will be accurate but that is providing the hex sides are true. Interesting but again, do you think this will be more accurate than marking out and drilling as I suggested?

Chris

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