MetalworkingFun Forum

I'm trying to make a between centers boring bar to use for boring the Sparey Dividing Head I've cast.
I'm not having much luck. I have drilled the centers in the ends twice, and when the bar is mounted between centers, I get .003" to .005" runout on the bar.The first time I cut the centers I used a flange type ER32 collet chuck that I made. I know it has .003" runout. I tried again with my 4 jaw independent chuck and got the same runout when mounted between centers.

The bar I'm using is from a platform roller on a treadmill. Lathe is an 10 year old Micromark 7x14.

Any ideas where I'm going wrong?

Chuck

My guess is to start at the beginning.  Is your tailstock aligned with the headstock?

(11-06-2014, 09:38 AM)JScott Wrote: [ -> ]My guess is to start at the beginning.  Is your tailstock aligned with the headstock?

That is where I'll start.

Chuck

Does it matter if there is runout?

(11-06-2014, 09:59 AM)f350ca Wrote: [ -> ]Does it matter if there is runout?

I don't know, to be honest! Does it?

Chuck

Just to make sure we're on the same page. Is this a bar that carries the cutter between the headstock and tail while the part being bored is mounted to the carnage?
If so runout shouldn't matter, your offsetting the cutter (effectively creating runout) to bore the hole.

It matters not a jot
The tool bit is excentric anyway , the tool tip care not if the bar dose not run true , it will still follow a circular path thus bore a true hole

There was a design that used a sliding dovetail arangmet to make the bar wobble this was to provide a fine adjustment of the cutter

Stuart

I agree with Greg if the cutter is mounted in the bar between centers and the part on the carriage the runout that you have doesn't matter, because the cutter is stationary in one spot between the centers

DA

Yup, what Greg, Stuart and David said.

Ed

Whew! It finally makes séance! Thanks for all the input.
Next decision is whether to make the spindle, and bore the hole to fit, or bore the head and turn the spindle to fit.

Chuck

edited to correct speeling