I would like to purchase my first mini-lathe but have one big remaining question. I primarily model tanks from WW2 so my needs are turning gun barrels and creating road wheels.
The complication I'm having is that I know I'm going to need a rotary table to perform some of the tasks when creating road wheels (i.e. cutting 7 holes perfectly spaced apart, among other things). I would really like to not have to buy a mill, b/c of space and money. A lathe is more realistic for my needs.
Since I know I will need a rotary table for some of my projects, my question is can a rotary table be mounted vertically to a mini-lathe?
Here's a suggestion which won't cost you any money. Reserve a copy of "Shop Savvy" at your local library, and when it comes in, check it out. He has both indexing attachment and shop-made milling attachment plans in there, all for a small home shop lathe. If you're used to HSM type plans with real blueprints, this will disappoint, but if you're any good as a model engineer you won't have any trouble. Lots of other fascinating reading in there too. His indexing attachment, like many others, uses a gear tooth and spring-loaded plunger to effect the indexing. A 28 tooth gear would be pretty handy for indexing 7 equally spaced holes, for example.
Grant's suggestion is a good one. While a rotary table is good for indexing any spacing, where they really shine is when you need to use it for milling. If, for example, you need to mill curved grooves. Or only partially around a hub. If you don't need the milling capabilities then building an indexing attachment will probably be better for you. If you build your own device then you can determine where all the clamping holes are. With a rotary you are kinda stuck with the T slots they come with. You can drill and tap other holes for clamping, but not through. Through holes will allow dirt to get into the works. But a faceplate for your lathe could be used as 1/2 of a home made indexing setup. ERS
I don't see a rotary table as a combination with a lathe. That's just introducing too much shummy in an already unstiff set-up. Besides, that would also imply a milling vice, and I can't see how to mount even the smallest rotary table on the typical milling vice for a lathe. But he doesn't need a rotary table. As Eric and Rex have pointed out, it is a question of layout and indexing. I made a very simple, yet effective indexing attachment (first for my 9" SB and later adapted to my
12" Clausing) lathe. I found/scrounged, some index plates with a 1.5" center hole. I then machined a simple little plunger stop. The index plate goes between the chuck and the spindle seat. This is okay since I don't do any turning. To make, say, seven holes evenly spaced on a wheel, say. Mount the wheel in the chuck. Use a pointy tool (e.g., a scriber). First mark the radius by holding the scriber against the work and rotating the chuck by hand. Then go to your first hole position and mark the cross point by using the cross feed. Back off, index to the next "7" position and repeat. Then center punch the cross points and drill the holes in the drill press. No problem holding it to a few thou accuracy. Better if you want to be really finicky. This is method is so easy and convenient that even though I have a rotary table, mills, spin-indexers, etc. When I want to mark stuff that's been worked on the lathe, rather than take it off the lathe and remount the work on another tool (e.g., a rotary table), I index it on the lathe using my cheapo indexer as above. It's a lot, lot, easier finding various indexing plates at a used machinery place than finding the right gears (pitch, bore, etc.).
I happen to have the cheap Enco spin indexer, and the minilathe. Here is what I find:
What is possible if the cross-slide is removed, leaving only the carriage base? The top of the dovetail on the minilathe cross-slide, to the spindle axis, is about 2.6 inches. The bottom of the spin indexer to the collet axis is about 2.75 inches. So apparently you could remove the cross slide from the minilathe carriage, and bolt on the indexer, with the minilathe axis about 0.15 inches below the indexer axis. So as long as your bolt circle radiuses are about 0.15 or more, this ought to work. You'd put the drill bit in the chuck, and hold and index the work in the indexer, and feed the drill with the carriage wheel.
Consider making your own special workholding jig for the purpose. Something that can be held in the toolpost, and index 8 holes in a given size piece, or whatever.
As long as the spindle axis is with about 1/2" of the indexer CL, you move the cross slide horizontally to get to the radius you need, then lock it down and index away. Am I missing something?
For most applications you could mount it directly to the carriage, after removing the cross slide. Or fashion a mount to the bed ways, perhaps from a tailpost base. The indexer has enough axial travel that you could use that instead of carriage travel to feed the work, for many applications including that of the OP.
I would make an adapter plate with slots milled/chiseled/filed roughly the shape of the ways, rig up a way to clamp it in place level and square to the ways, then oil the ways and fill the space between them and the plate with metal-filled epoxy. Based on considerable recent experience making parts with the stuff I'd expect to trim the overflow while still soft, let it harden and add more to fill the gaps, several times.
It could be as simple as clamping it to the flats between the V-ways. But you may have to fabricate something. In an earlier message I suggested you might want to buy a replacement tailstock base to make a mount from. As John Martin pointed out, 7 doesn't go into 360 degrees evenly. If you decide you need the precision then the cheap indexer won't do. You would need an indexer with a index plate that has a number of holes divisible by seven. It may be possible to get a replacement index plate for that Enco that has the right number of holes. Anyone know if that is possible?
The spindle does have a few inches of extra length, but it doesn't appear to permit controlled axial motion. When you loosen the setscrew collar to let the spindle travel axially, you have nothing holding the rotational position. Attaching to the carriage bed would seem to be simplest method; you'd also have the carriage wheel to control feed rate and pressure, instead of just shoving it with your hand.