Laying out a bolt circle?

The Machinery handbook has table of jig bore coorinate, if you are going to use a mill machine, page 78 of my 15th edition. Value are not given for four holes since moving on the x and y axis the radius from center is all that nessacery. 3,5,---12 are given in my book. Multiply the value showen by the pitch circle.

Give me your e-mail and i will send you a bolt hole and trig program. Tim

Me too please? My posted address works.

Ken.

Ken your email address is spammotel?

Yes. It is a forwarding service and the name spooks spammers.

Ken.

Dave, I have an "indexing ring" on the bullgear directly behind the chuck on my lathe (Atlas 12") with 60 holes. Every 15 holes, scribe a line across the 6" circle you have. You may not have the indexing ring on your lathe, but I think in one of the posts you mentioned a degree ring on the chuck - every 90 degrees... Maybe I'm not seeing the entire picture. Ken.

That program sounds like a good candidate for the Dropbox, Tim.

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Lay it all out after it's chucked up in the lathe. Scribe the circle by using the crossfeed micrometer to set the radius as you described, then set the scribing tool as near as you can to vertical center. Use the division pin stop in the lathe headstock to lock the chuck and cross scribe with the crossfeed. Turn the chuck 180 degrees and lock again. Repeat the scribe mark to confirm that it is centered. Rotate 90 degrees and repeat for the other two holes. This procedure works for any bolt circle that is divisible by the number of stop pin holes in the headstock, usually 64. Bugs

my spamcop.net address is also real, and I'd like to think has similar effects if any of the spam harvesters are still manual. They block

98-99% of my incoming spam for me.

If I do, I haven't noticed it. It's a Rockwell 14", mostly like this:

as long as I can use the degrees marked on the chuck, and lock the spindle at the right points, I should get good accuracy in my marks.

Thanks, Dave

You could thread some studs into the holes and then support the studs on some 1-2-3 blocks on a surface plate with the disk vertical. If you still have your center mark on the disk, you can use a square on the surface plate to mark the other two holes.

Regards, Ed

OK then, once you've done the scribing, rotate the toolpost ( if a two or four way ), or use another toolholder if you have a QCTP. In place of a tool, insert a bit of 1" sq. bar through which you have previously (note the catch?) drilled a hole using a 1/4" drillbit held in the lathe chuck, thereby ensuring the hole is exactly at centre height. Once drilled, mark the top of the bar ao it never goes in upside down. Now you can bring this up to your marks with a 1/4" body centre drill inserted & use the cross slide to position the centre drill on the PCD. Turn the centre drill with a cordless drill to start each hole, then complete on the drill press. Or you could make a Dremel mount to fit at centre height in the toolpost & drill the holes directly with that Or George Thomas' book the "ME Workshop Manual" has plans for a toolpost mounted hand turned spotting drill.

Or, if you are brave enough, try " Sigh... what I really need to do this easily love, is a jig borer. There's one on Ebay in Czechoslovakia for only $1500. We could spend a week there, I hear the Skoda works is worth a look"

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A good approach. However -- not all lathes have stop pin hols in the headstock. My 12x24" Clausing certainly does not.

Enjoy, DoN.

If you work in IT, the quick and dirty way is to do a quick actual size CAD plot and glue the paper to the workpiece as a template. "Good enough" in many cases.

Got a 4-way, yes.

So, the height is constrained by the nature of the tool holder, and the alignment is taken care of by making sure the bar is flush against the work. Only trick is getting it aligned to drill the original hole, which I should be able to reference against - what, the face of the chuck?

So is this voice of experience here, or are you making this up on the fly? Either way, it's impressive. The big problem with making this up as I go along is that I haven't been exposed to creative techniques like this, but of course once explained they make perfect sense.

So "spotting drill" is the critical term here?

I think I'll stay with the home-made stuff, at least for now.

Thanks, Dave Hinz

3-M spray adhesive. I figured when I asked this, that I'd get a half-dozen good responses. I underestimated by quite a bit.

Well, I've not drilled directly like this, but I have used a 1/4" punch made from silver steel ( drill rod in USA) through the hole in the bar. A slight tap from a small hammer, when the punch is properly aligned with the scribed marks is sufficient for the drill to pick up in a drill press.

Having said all that, I wouldn't have thought that the precision necessary just for a caliper retracter would require more than scribing the marks in the lathe & then centre punching & drilling in the usual way? My rear calipers ( what a stupid bloody idea on a road car rear discs are by the way!) are retracted using a nice simple 12mm Allen key, so no need to have to make special tools. My wifes' old VW Golf GTI had a a pair of recesses in the pistons - I used to use a pin spanner made by drilling the jaws of a cheapo Chinese adjustable spanner & pressing in a dowel of silver steel to each jaw for those - worked for 157,000 miles!!!

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Well, the problem came up in that I really needed all 4 pins, but only made 2 marks initially thinking that would do, and by the time I knew I needed 4 pins my initial 2 points were gone, so getting the angle became...inconvenient...

Why? Lots less complexity and unsprung weight than (shudder) drums...

The Saabs use a 5mm allen wrench to retract the rear pistons, or maybe a

7mm. Can never remember, but it's on the shelf of "special brake-job tools" that I visit once a year or whatever.

There ya go. I sure like being able to go downstairs into the shop, and make something that looks reasonably professional, to take care of an otherwise expensive or unsolvable obstacle to a project, from whatever I happen to have on hand. Especially nice when it looks good.