Q. about drilling/bench drill/technique

[rvt]

This is a problem that I come across frequently. I can get around it by using a hand drill and fiddling around it it, which doesn't make it as messy as you might think with a little patience, but it's far from ideal and has lots of risks involved with the parts I'm using.

Basically, I have trouble drilling at an odd angle. I have to counter sink a small hole, but the whole runs through 'two levels' of a metal ring (it has to be there, no way around it). It's not bang in the middle either, it just catches the one higher leve, but unless I can drill that out there is no way I can countersink it, which it needs to be.

I have a big old bench drill, with a not very smooth one level handle. No ideal for small things like this, at all. Tried it once, very slowly, at the drill bit just bends out to the side and it even snapped in the end.

Small diagram to try and explain the idea.


I can't afford any new machinery right now (still haven't had the lathe pay for it's self yet), but do you have any advise on (a) technique and (b) the 'right tool for the job'?

Thanks for your time!

[DMIOM]

do you need to countersink (for a countersunk head) or counterbore (for a socket-head cap screw?)

If its counterbore, you can get them with a pilot - so that engages with the smaller hole and keeps it on-line through the interrupted cut.

Even if you want to countersink, you could maybe use a counterbore to clear a gully down through the upper ring.

Another (non-piloted) option might a small end-mill - that has the cutting edges near-enough to 90 degrees to the axis, rather than the sloping shoulders of a drill bit which will force it off line. Then, either plunge it in. or approach the job from the free side until you're far enough in, then plunge if necessary.

Dave

[rvt]

Thanks for your thoughts Dave.

It's countersink, I don't think there is enough depth to counterbore, but anyway the screws are countersunk so it makes sense.

I've looked, but can't find an actual countersinking bit that will be small enough? It really does need to be quite small otherwise it can catch on other parts of the ring (probably not drawn out particularly well above)

I think the other problem is that I don't have any sort of clamps for holding the piece in place. If I did, perhaps a countersinker/borer would work well?

I'm looking at a 'cheap' micro mill of sorts, thinking it might be more versitile than simply buying a mini bench drill of sorts.

[DMIOM]

If you're just drilling it, you may find its a help to use a centre drill (if you can one of the right dimensions!), as the solid body will hold it more rigid.

Clamps don't have to be sophisticated, in fact two pieces of wood with a suitable hole in the upper one, and just woodscrews to hold them tight and sandwich your workpiece, might be a useful 'fixture' to hold it whilst working on it ...

[rvt]

I correct myself, it is a mortising drill, not a pillar drill. But anyway, you have inspired me to try and get what I can out of it. I'm going to take it off tomorrow and clean it down and lubricate things. I'm going to then put it on a more sturdy surface, by the lathe. I've found an 'M3 counterbore', which is as close as i can get and i think will work pretty well at taking off the bit I need. I measure the heads, they're 2.77mm diameter, so it should work okay.

I'm then going to try and create some sort of clamp out of wood, like you suggest. I'm optimistic!

[Bearcar1]

Hello RTV, is it possible to drill your holes and counterbore/sink etc. before you machine these pieces. That is to say layout and drill the holes first and then do the final machining.


BC1
Jim

[DMIOM]

That's a good point from Jim.

........ I've found an 'M3 counterbore', which is as close as i can get and i think will work pretty well at taking off the bit I need. I measure the heads, they're 2.77mm diameter, so it should work okay......

Just a caution - it would be worth checking the dimensions, as an M3 counterbore may be one for an M3 SHCS - so the pilot will be just under 3mm for the shank, and the cutting part will be larger diameter to make the pocket to hold the head of an M3 SHCS.

If you are able to share any more information (what the part's made of and a dimensioned drawing - and maybe even a photograph!) the collective may be able to come up with other suggestions as well.

Dave

[rvt]

Again, thanks for your thoughts!

Jim, good idea, but sadly not possible. The way I state above is the way it has to be done. I do projects of adapting various different slr lenses to fit different mounts, this involves using some standard parts/mounts that i cannot machine myself. But thank you for the suggestion.

Dave, the M3 counterbore I was looking at is this one. From the description, I'm thinking the 'max diameter' (ie where it cuts) is the M3 size??

I don't actually have such parts available to photograph at the moment. They come up frequently, but not right this minute , hence the (poor!) diagram. Will try and get something soon though.

I've been thinking more about how to mount/hold the piece that needs drilling. These are generally small rings or tubes made of soft metals (aluminium, brass) and need drilling at 4 to 8 points around the ring (this is most common, atleast). I'm thinking a vise of some sort would probably be a good investment and would make the job quicker/easier/more efficient (rather than building something myself that might not work for every piece). I'm unsure as to whether to get a rotary table with a 80mm chuck in (like my lathe). As the rings are made of soft metal, perhaps this would not be ideal, as I generally can't grip them too hard without distorting them (no problem on a lathe I've found). But perhaps with the downwards pressure of a drill, it might not be good enough. (eg: like this)

So perhaps a swivel vice of sorts would be a better option? The problem then is the grip is even more uneven. The rings are sometimes threaded, so if i could make a tube of sorts that could first go into the vice the ring could just be held in place, and then moved around with ease. Really not sure.

I cleaned everything out today and put the big thing on a better surface. I will take some photos later so you get an idea of the monster I'm working with ;)

[rvt]

Shows how it was originally intended to be set up. I think with that plate of wood off, it seems that attaching a vice of sorts would be pretty straight forward?

[andyf]

Just a thought:

Going back to your original diagram, I wonder if you could take a plate as thick as the step and bore a hole in it which was a close fit on the step, then put it on the widget you are modifying to offer a flat surface for the drill and counterbore. It would be sacrifical, but you would be able to keep rotating it until you ran out of room for more holes.

I suppose it would best be made of the same material, to stop the drill trying to wander off into the softer side, and I am assuming that you have access to a lathe or milling machine to bore out the hole in it.

Andy

[75Plus]

While Andy was writing I was sketching. Both our ideas are similar I think. here is mine.

Using a piece of a solid material such as ally or even acrylic, large enough to be clamped to the DP table, turn a  slight indention that is a snug fit for the piece being worked on. This piece could be square or rectangular if you have a 4 jaw chuck. Make another piece that has a spigot that will fit in the ID of the work piece. These two parts can be screwed together to form the clamp you need and the base part can be clamped to the DP table.

Now, in order to locate the work piece for drilling, take a piece of rod the diameter of the desired hole and file a flat on one side the width that you want to cut into the upper piece. Place the clamped work piece against the flat and secure it to the DP table. Replace the rod with a drill and go.

I have tried to show the parts I mentioned in this sketch. I hope they make it more understandable.

Joe

[rvt]

Just a notice to say a final thank you for your thoughts on this problem. I'm now have no trouble with such 'difficult' cuts. As was suggested, securing your workpiece really is essential, and with a very basic mini clamping set I now have no trouble. For the situations where there is a lot to cut through at this stange angle, I also have some end mills now, which do the job perfectly. Thanks!