Thread: How to bore this tool holder?

Hi Chris,
Could you put a centre in the headstock and tailstock then hold the piece between them while you clamp it in the tool post.

Phil

Phil,
I could put a centre in the tailstock, but I don't think any of my centres are long enough to protrude through my 4 jaw chuck (I assume you meant 'chuck' and not 'tool post'?). I'll check though.
Chris

Perhaps hold the work in the tool-post and clamp the boring bar in the 4-jaw using the ability to offset the 4-jaw to adjust the depth of cut (same principle as the boring head on a mill - sort of)

Other ways that come to mind are
Buy the bigger drill
slow process of adjustable reamer

As I have this road to go down yet I'll be interested to see what answers suggestions are made.

Gavin,
the method you describe is mentioned in the book Basic Lathework by Stan Bray. It might be an option.

wheelinround,
a decent quality 20mm drill bit is expensive and may produce an oversize hole. A slightly oversize hole might be OK as I am going to slit the mounting block and fit cap screws so I can tighten the holder on the grinder. An adjustable reamer that size would be expensive too I guess.

Chuck this in the 4 jaw and sweep around the bore you've drilled to get it on centre. Then turn the chuck to position the step you've machined closest to you and indicate along it to ensure it's parallel to the lathe's ways. Indicate both the bottom surface that will be on the bottom surface of your tool post, and the surface that will be registering against the side of the tool post. It doesn't matter if the hole you're drilled already is parallel to the ways or not, what you're more concerned about is boring a hole parallel to where it's held. Of these the bottom face is most critical, otherwise the tool will be "cocked up/down". Simply bore it out with a boring bar, the bore will be parallel with the toolpost when mounted. A bore is always parallel to the machine's ways, the trick is to ensure the bore is parallel to anything else on your work that's important, in this case it's the step that's securing it.

Just for info, I have a Proxxon that I made a tool holder for and found it makes a poor accessory for cross drilling etc. It's a Dremel style and yours is clearly more powerful, but mine just doesn't have the guts to be cross drilling in steel.

Pete

Edit: Hopefully all that makes sense. It's the best description I can manage I'm afraid, try not to over think it Chris, go with your initial gut feeling as it was right, and this is a simple boring job. You can adjust centre height if you screw it up with shims or QCTP holder adjustment if you have a QCTP, likewise can always pivot the tool post if that's not quite right, you do however want to try to ensure it's not cocked up/down however.

The description below from Phil is the alternative way to bore it, and indeed how I did my Proxxon holder as it just so happens. However I had a boring head (which I don't think you have right?) so that made the job much easier than trying to hold a boring bar in a 4 jaw. Holding it in the toolpost and boring it will guarantee on centre, and parallel, but requires the tool to be held in the 4 jaw. The alternative I described above requires more accurate setup but is a straight forward boring job from there. Dealer's choice which way you choose to go.

Originally Posted by jack620

Phil,
I could put a centre in the tailstock, but I don't think any of my centres are long enough to protrude through my 4 jaw chuck (I assume you meant 'chuck' and not 'tool post'?). I'll check though.
Chris

Hi Chris,
Take the four jaw off for the setup only. Then suspend the job between the two centers in the hole you have drilled. Bring the tool post up to the job and mount it like in your pic. The job will then be on centre. Remove the headstock and tailstock centers and replace the 4 jaw or even a 3 jaw and put the boring bar in the chuck. Use a dial indicator to measure how far the tool is sticking out of the boring bar for each cut.
Let me know of you need clarification as I recognize I am the explainer from hell.

Phil

Was there any particular reason why you machined the step for the holder 1st.

If you had covered your bases prior to placing the step on the block you more than likely would not have this slight problem now.

If you have a suitable piece of bar that you can drill to accept a piece of round or square tool steel there wont be any great problem.

Set the bar in your lathe 3 jaw chuck if its bright,if not wouldn't be a bad idea to place in the 4 jaw and clean it up.

Centre drill one or both ends if you wish,work out where you need your tool positioned for the bore,drill this hole to suit tool steel,and drill another hole for a grub screw to lock onto your piece of tool steel.

Sharpen your tool steel to suit your material,and adjust the tool steel until you have your finish bore size,easiest way would be to use a micrometer,just crack the grub screw and lightly tap the tool steel out to desired size.

Doesn't really matter apart from appearance if the boring bar is not running true as long as its not running out more than your finished bore size.

For what your doing and the fact that your splitting it after boring you could use either a pair of verniers or inside calipers to measure the bore whilst the whole thing is still set up.

If you feel you would need to remove the bar to measure then turning between centres would be the preferred option.

With clamping blocks it is a good idea to bore/drill under size, then split and fit clamping bolts with shims in the slit.
The hole is likely to close up on most materials if you bore to final size then cut.

Mark

Originally Posted by jack620

I'm making a poor man's toolpost grinder/cross-drilling attachment from a Proxxon die grinder. The neck on the grinder is 20mm diameter. I have drilled the holder to 18.5mm, which is the largest drill bit I have. I need to bore out the last 1.5mm.

The most accurate way to do this would be between centres, but I don't have a between-centres boring bar. Have you guys ever made one?
Chris

I don't see what the issue is here.

You've already drilled it out to 18.5 mm, and the 4 jaw chuck or whatever you used was obviously accurate enough to do this.

Why the big issue on using a boring bar with the same setup ?

I don't see why you doubt the accuracy of a boring bar?

Looks pretty straight forward to me.

Rob

Hi Rob I think it might be for cross drilling on centre not the boring bar that the accuracy is required.

Phil

Originally Posted by Steamwhisperer

Hi Rob I think it might be for cross drilling on centre not the boring bar that the accuracy is required.

Phil

I don't see why he doesn't just do what Gavin suggested.

Rob

PeteF,
thanks for the explanation. Your'e right about getting the bore parallel to the bottom of the holder- that's critical. I'm sorry to hear you proxxon is no good as a cross-drilling machine. I hope mine fares better.

Edit: no I don't have a boring head, but I do have a set of TC boring bars to fit a boring head.

Phil,
Now I get you. I don't need to bother with the centres because I haven't changed anything in the setup since I drilled the hole, so it's already on centre as long as it stays mounted in the 4-way TP.

pipeclay,
I milled the step first so I could mount the holder in my toolpost, thereby guaranteeing the hole would be on centre and parallel to the ways. I currently don't have a QCTP, and I hate shimming, so I wanted the holder to go straight into the toolpost and be on centre. Unfortunately I didn't give enough thought to how I was going to bore to final size. I like the idea of the between centres boring bar. I have some 16mm 12L14. I think that would need to be turned down a little to provide chip clearance in the 20mm bore.

Rob,
I used a 16mm keyless drill chuck in the headstock to drill the hole in steps. I have no idea where you got the idea that I doubt the accuracy of a boring bar. My question was what type of bar to use and in what setup. I'm glad it's straightforward to you though.

Chris

Originally Posted by jack620

Gavin,
the method you describe is mentioned in the book Basic Lathework by Stan Bray. It might be an option.

wheelinround,
a decent quality 20mm drill bit is expensive and may produce an oversize hole. A slightly oversize hole might be OK as I am going to slit the mounting block and fit cap screws so I can tighten the holder on the grinder. An adjustable reamer that size would be expensive too I guess.

Totally understand Suttons Drill bits upwards of $50 and even Suttons these days are proving not worthy.
H&F $25 Doesn't seem that bad https://www.machineryhouse.com.au/D314 for a drill bit M2
a reamer little bit more https://www.machineryhouse.com.au/R726

If you intend slitting the hole why such in doing so its going to be slightly out of round when bolted together.

May I suggest you take a look at Bill Ooms tool post drilling attachment