Drilling around the circumference without RT

Gallery, Projects and General > How do I??

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NickG:
I was going to suggest the same method Dave did using the chuck jaws. I've used this method a few times, infact I used it for my chuck back plate and it worked spot on.

I would scribe the circumference with a sharp tool as you said then scribe 3 lines crossing that circumference using the cross slide, indexing with each chuck jaw. Then transfer to mill or drill for drilling.

Nick

raynerd:

--- Quote from: kvom on July 08, 2009, 04:39:37 PM ---Assuming you can clamp the bar on the mill vise and locate the center, then a bit of trig and the dials/dro will get you there.

--- End quote ---

Kvom - was thinking about this a last night in bed (is that a bit sad? ::))

NickG - that is a great idea - could then also check it with trig as a double check!

Hummm interesting - I was 90% sure I was going to purchase a RT this evening but you have made me think again now. I will get one, just ideally not this month.

kvom:
If the trig i too challenging, then Machinery's Handbook has bolt circle X-Y formulas for any number of holes.

raynerd:
Well I have given it ago but it has been a while since I did trig. last! I have expressed co-ordinates in terms of x, -x, y and -y from the centre point of the bar and expressed the answers in terms of d and therefore they should work with any pitch circle diameter that the holes are to be drilled at 120deg intervals.

You can hopefully see what I did from my workings below:

Hole 1
X= 0
Y= d/2

Hole 2
X= 0.433d
Y= -0.25d

Hole 3
X= -0.433d
Y= -0.25d

I haven`t a clue if it is correct, my dad seemed to agree with me which is a start! :smart: I am curious to know how accurate this will be using the DRO on my mill!! Perhaps the opportunity for using it as a necessity for the first time!

Chris

DavesWimshurst:
Looks good. :smart:

With DRO should be easy, without don't let backlash in your feed screws and having to read backwards for one of your feed directions trip you up.
Nice C-O-M!
Dave

M for math.

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