Long Division

[Allen Smithee]

In my brief description of making an external hone I started straying into my very slow build of two dividing heads - a headstock divider for my myford S7 and a Versatile Dividing Head, both to the popular GHT designs. In both cases they are projects that were started by others - the headstock divider was given to me part-built by the nice old biddy who sold me my lathe, while the VDH came indirectly from an auction site (a friend of mine "won" an auction for two and sold one of them to me). Many people have built and documented building both of these far better than I would, so this thread will be the occasional documenting of just the interesting things I come across the way - especially any learning points which might be useful to others.

For the "story so far" - the headstock divider currently looks like this:



It will share the dividing disk, sector arms, indexing plunger with the VDH (and potentially the microdivider and associated second wormwheel if required), which is why these two dividers are being built together rather than as two separate jobs. The VDH parts look like this:



As you can see in the photo above, I have finalised the mountings and I'm very near completion on the Headstock divider, because this will be used to drill the holes in the dividing disks. I'm very close to the point where making the disks will be the next job. GHT suggests several ways to do this, and I'm leaning towards the idea of drilling these in the lathe using the headstock divider, but that means I need a toolpost drilling facility. I'm wondering if mounting a dremel-type tool on the toolpost would do this for me - anyone have any thoughts?

AS

[Allen Smithee]

So this evening I turned my mind to this toolpost drilling concept. I have four of the "dremel" rotary tools - one original mains dremel, a couple of cheapo cordless ones and a mains one that came from Warco. The dremel is too useful elsewhere, but of the others the Warco one has the least radial play in the shaft, and it also has the same nose-collar thread (roughly 3/4"x12tpi) as the dremel allowing me to change my mind later!

So I decided to base my setup on this drill. I want the mount to go onto my Dickson QCTP, so I needed to fabricate something which attached one to t'other. Some years ago I bought a cheap DIY-type drill press - the cheapo thing that mounts a normal black & decker as a basic drill press. It was under a tenner from (IIRC) Lidl and I had vague ideas about using it to make a sort of simplified Universal Pillar Tool, but it wasn't stiff enough to make it worth the effort. But at the heart of this thing was a die casting that had potential:



Obviously step 1 was to make a collar that fitted into the clamp ring with a 3/4x12 tapped hole in the middle. I found a nice chunk of alloy bar and made this:



This was my first serious attempt at internal screwcutting a large, coarse pitch thread. I used the "set the topslide at 60 degrees and advance on the compound" method, made lots of mistakes and learned a lot. But the result is serviceable and holds the drill firmly:




So then I just needed to trim off the unwanted parts of the die-casting, initially in the bandsaw and then milled to give a flat area in the middle with with a hoggling bit. The result looks like this:




All I now need to do is mount a piece of 10mm sq steel on the back to fit into a Dickson tool-holder, but I ran out of time. Then I need to find a centre drill small enough to fit its largest collet and I'm in business...

AS

[cnr6400]

Hi AS, How big are the holes to be in your plates? Are the plates steel? How many holes?

Reason I ask is that any drilling I have tried with a few kinds of Dremel type tools seems to end badly due to three things - lack of thrust bearings in some tools, rapid bearing wear / wobbly drills , and collets wearing out fast. In steel all the above happens faster than with soft materials.

Hope your experience is far different and better than mine.

If not, I would recommend finding a friend with a mill that has a DRO to drill your plates, or for the lathe, build a ball bearing spindle with thrust takeup and a good chuck. You could power it with a cordless or corded drill or compressed air drill as motor, with V belt or toothed belt drive. There is a book about spindles in the Workshop Practice series by Harprit Sandhu with some good suggestions on spindles.   

[Allen Smithee]

Thanks for the tip! I'll try it, and if I get problems I'll try something else. It would still be useful as a toolpost grinder.

In principle I could use exactly the same fixture to mount a black & decker in the toolpost, but I think the bearings wouldn't be tight enough for any accurate drilling.

AS

[Roger B]

Why don't you use the Dremel system to spot all the holes and then finish off with a conventional bench drill?

[Allen Smithee]

That's another option, yes.

PDR

[Allen Smithee]

Well the finished article looks like this, and it feels surprisingly stiff:





I gave it a quick try-out drilling some holes in a bit of nylon bar and a bit of HE15 - seemed to work well enough, although I take cnr's point about how long it might last drilling in steel. It also fits on the other face of the toolpost, for drilling radial holes.Even if it only drills soft materials I can still use it in conjunction with the headstock divider to making indexing disks for the basic indexer I made for my mill. It could also be used as an internal/external polisher, and as the bearings have no detectable axial play I may even see how well it works as a toolpost grinder (although that's something I hate doing because of the amount of effort involved in covering up the ways etc).

And I can always try using it to just spot the holes as Roger suggested. I'm not sure how accurate the hole positions end up doing that, but I can find out.

AS

[awake]

Looks good! I look forward to hearing how you wind up putting it to use.