spiral spindle cutter

Don't mess with a flimsy Dremel. You can buy a router motor with spindle and ER11 collet chuck for $30 (15 quid) on Aliexpress, shipped.  **LINK**   That will hold a standard 1/4" shank cutter. If you want a more powerful .500kw motor, that's an extra $20.

Edited By Hopper on 21/06/2018 08:01:36

Edited By Hopper on 21/06/2018 08:02:16

Thanks for that last batch of posts. I'll try to answer them all in one.

re a CNC approach. I considered the idea. Seems cheap and accurate and compact. The problem is I have zero experience of stepper motors, controllers, interfaces and control software. I wouldn't completely dismiss it but the learning curve would be VERY steep.

re a router motor - an excellent idea. If I go the home made route then a dremel will probably be easier but if using a lathe with a cross slide and toolpost I might well do this. Having said that, my rotary too is a 550w vonhaius dremel-compatible, so not that flimsy.

re accuracy, yes i'm concerned about accuracy with the dremel on a home-made unit on multiple passes. I was hoping i could do them in one pass as my stock isn't that thick and for instance I might be able to do hollow spirals with a narrow through cutter and finish with a fluted and that kind of thing.

My preferred option so far would be would be a mini metalwork lathe if i could get the gears to give me the pitches I need (and probably with the router motor as suggested above). Its a bit expensive for me but then I'd have the joy of full lathe operations to play with. I'm just not sure theres anything available off the shelf and I'd have to be sure I could get the gearing i needed.

oh, and here's where I am with draft 1 of the home made solution... still some way to go but just so we can see we are on the same page:

I found this while surfing. It's opened my mind up a bit more to stepper motor control rather than syncing spindle and leadscrew and customsing gears. It's still outside my skill zone but there's so much information and support out there on the topic (especially arduino control) I'm going to explore it a bit more. I think you'll find his blog interesting:

http://blog.pdxtex.com/p/router-lathe-build.html

I really think your best bet for this project is a used, old style British type, metal working hobby lathe such as an early Drummond or Myford which regularly come up on ebay. Most have an 8tpi leadscrew. It really depends on the lead ( the horizontal distance between each "thread" that you are after. In order to generate long leads you need large driver gears and small driven gears. With a standard set of gear wheels as supplied with the sort of lathe mentioned above, 20-65 in steps of 5, then the longest lead you can get is about 1.8 inches. With a few extra gears you can increase the lead - the longest I can get on my Myford S7 is about 5 inches. The gear calculation is easy, just multiply the drivers together, multiply the driven gears together. Divide the drivens into the drivers and divide by the pitch of the leadscrew e.g. (55x60x65) / (20x25x30) / 8 = 1.79. If you have an extra 20 and a 70 then you can get to nearly 3.5 inches (60x65x70) / (20x20x25) / 8 = 3.41. Some juggling of the relative positions of the drivers and drivens would be necessary to get the various combinations to mesh but the principle is sound.

The state of wear on the lathe is largely immaterial for your purpose and it would not need a motor - with long leads you drive the saddle using a handle on the end of the leadscrew.

Just a thought,

Rod

Easiest way might be a mini-lathe as you could design a new banjo with an extra slot and get it laser cut from 4mm plate.