Thread: How to bore this tool holder?

Thanks for the links Phil. Those drill bits are cheaper than I thought. Bill Ooms has some interesting looking attachments. If the Proxxon is a failure I might have a crack at Bill's drilling attachment.
Chris

Thanks for all your replies gents. I will have a go at Gavin's boring-bar-in-the-4 jaw idea. If I can't make that work with the boring bars I have I will make a between-centres boring bar as per pipeclay's method.
Chris

Originally Posted by Gavin Newman

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)

Nice one Gavin, very clever solution, the resulting hole will be bored exactly centered on the chuck center and on the lathe axis...

Regards
Ray

Originally Posted by jack620

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

Chris it all seemed to be getting over complicated in the discussion.

A basic boring bar in the 4 jaw seems like a good way to do it. It's just one step up on what you've done to this point.

The tricky bit will be getting the cutting arc diameter just right.

It might be easier (less chance of error) if you machined up some round bar to the drilled hole dimension, reduced one end so it can go in your drill chuck in the tailstock.


Then use that as a guide to center and square the block in the four jaw, remove the round stock, and use a boring bar on the toolpost in the normal way.

Rob

Hi Chris,
The 4 jaw trick should work fine, you can do your final adjustments (assuming your using a HSS boring bar) by moving the bit in the bar, use a DI or mic to carefully adjust the size.

I have a few large drills from CTC, these are cheap and ok for the odd job but certainly not top quality.

Thanks Rob and Ewan.

The 1/2" boring bar plus a few mm of tool protrusion will mean very little offset (if any) is required to get to 20mm.

Yes Ewan, I have a boring bar with an adjustable HSS tip.

This will all have to wait for the weekend. Will report back then.

Chris

I finished this job off today. I ended up just mounting the boring bar in a 1/2" ER40 collet and adjusting the tool bit to achieve the correct diameter bore. It worked very well. Surprisingly the hole didn't close up after slitting. Thanks for the help.
Chris

Looks good, and glad to hear it all worked out for you.

Dave

Looks good Chris, Gavin's suggestion looks to have worked out fine..

Now the $64 dollar question, how does it work as a tool post grinder? I'd be hopeful that you might be able to do some internal grinding with such a set up..

Regards
Ray

Likewise, how do you find it for cross drilling in steel? As I say, mine is smaller and struggles, I wonder how your larger one goes?

Pete

Ray,
I've never actually had the need for a TP grinder. Maybe I'll discover one now!

Pete,
I reckon it would struggle with anything other than sub-1.5mm holes in steel. It only has a 100W motor. My intended use is for fluting, slitting and cross-drilling brass and aluminium for model engine making. I will report back with results.

Chris

Cool. The nose of my proxxon also has only a very small area to grip by, which doesn't lead to a very stable setup at all. It looks like yours is far more suitable for the task.

Pete

Hi Chris, result looks good. Having looked at lots of responses here, I thought this little gem would also have been a contender. It's called a PRACTOOL SUPER DRILL. (high faluting name for a slightly different Boring Bar). I found it at a field day in the bush somewhere 20yrs ago. Basically it's bores from 1/2" to a bit over 1'' using the small end and up to about 3'' using the 1" section of the arbour. The HSS tool steel is adjustable in the bar. Someone else can tell us how the 'square' holes were bored for the tool bits. It comes with a gauge to set the tool bits.

Hope this wasn't too 'boring' for the micro-brigade!

Regards, Daryl

Thanks Daryl. The setting gauge is a good idea. I tried using dial calipers, but found it very difficult. A depth gauge that straddles the tool bit would probably be the most accurate way of setting it.
Chris

You can use a standard mic to measure the cutting increase. Obviously you need to allow for half the boring bar's thickness to calculate the radius, hence the bore diameter. In reality however I find I'm only after an increased cut of xxx, and measure off the finished bore, the mic is there simply to control the amount of feed. For occasional use that's fine, and I'm happy to do that, but carbide cutting tools on my nice mic faces doesn't impress me. I've seen some people make up a gauge, imagine a C-clamp with the screw replaced with a bolt (indeed as I wrote that it gave me the idea to sacrifice a cheap C-clamp, cut off the screw and retap it for a standard metric bolt. I'll try that next time I need to do this). Put a lock nut on the bolt (outside of the C), and each time you need to increase the depth back off the bolt. Measure with telescoping gauges just as you would measure the bore.

Pete