spiral spindle cutter

[john constableParticipant @johnconstable10725]

Thanks for those kind word, Larry.

Sometimes these enforced life changes are a blessing in disguise. In 2011 I left hospital in a wheelchair after having a brain haemorrhage, my wife left me and a few weeks later I was made redundant. Looking back its difficult to see how I survived all that or see anything positive in it. However, I didn't like working for that company and I probably still would be (although last year they went under!) and I am clearly better off without my wife. Friends have disappeared into the woodwork but they've been replaced with a better class of people who are worth knowing. And, best of all, its given me time to take up things I've always loved or wanted to do like my woodworking. And, to be honest, the idea of working in small scale actually appeals to me. Boxes and clocks were always on my project wish list. So, it could be worse!

[john constableParticipant @johnconstable10725]

Posted by JasonB on 20/06/2018 19:20:12:

Not the best video but much the same as the mini lathe one I posted earlier. 5:1 using the banjo gear train and then putting it through the gearbox brought it upto 10:1 so 10 x 0.125" = 1.25" per turn of the work. Does need a lot of effort to turn the leadscrew so a decent handle would certainly be needed.

like that – like that a lot. What would it take to get a lower pitch?

[john constableParticipant @johnconstable10725]

Posted by Brian G on 20/06/2018 19:18:53:

Yes John, I was suggesting linking the two threaded rods together (regardless of whether the first rod is connected to the spindle by gears or chain) so that they turned in sync when one was turned with a handle. That way, you could just fix nuts to the carriage and not need to bother with any kind of sliders. The real cheat's method would be tee nuts (**LINK**) which could just be hammered into both ends of wooden blocks.

I'm with you on the difficulties of working from a wheelchair, but I am lucky in that my paralysis is intermittent, so although I keep a few hand tools by my desk, I generally work on drawings (or 3d models for printing) whilst paralysed and make things when I can move. Generally I talk my son through the machining and stick to the bench work.

Brian

I'd need to line up the nuts very carefully so tnuts might be a bit tricky to get perfectly square to the rods.

[Brian GParticipant @briang]

If you used separate blocks to mount each T nut you could thread them onto the rods spaced the right distance apart, then screw them to the carriage. Position wouldn't be critical as long as the blocks laid flat against it. (I used to work in quality, it is often cheaper and more reliable to use a design that absorbs errors than to try and eliminate them – either that or I am just a bodge artist).

Brian

[john constableParticipant @johnconstable10725]

[JasonBModerator @jasonb]

Posted by john constable on 20/06/2018 20:17:44:

. What would it take to get a lower pitch?

do you mean a higher pitch where the pen moves along the work even more, If so then More gears and bigger ones too though there comes a time when they simply won't fit on the bracket (banjo) so a longer one would be needed.

Lower pitch becoming more like a screw would be easy just by altering the gears supplied with the machine.

If you want a very low pitch spiral then maybe forget this method and get a wood lathe and Sorby spiral tool, the coarse wheel gives a nice shallow spiral. In engineering terms this is a bit like free hobing in reverse.

[john constableParticipant @johnconstable10725]

Posted by JasonB on 20/06/2018 21:10:14:

Posted by john constable on 20/06/2018 20:17:44:

. What would it take to get a lower pitch?

do you mean a higher pitch where the pen moves along the work even more, If so then More gears and bigger ones too though there comes a time when they simply won't fit on the bracket (banjo) so a longer one would be needed.

Lower pitch becoming more like a screw would be easy just by altering the gears supplied with the machine.

If you want a very low pitch spiral then maybe forget this method and get a wood lathe and Sorby spiral tool, the coarse wheel gives a nice shallow spiral. In engineering terms this is a bit like free hobing in reverse.

yes higher pitch – less thread-like. someone mentioned that you could reverse the wheels on the banjo to go higher.

[john constableParticipant @johnconstable10725]

I'm having trouble posting a jpeg. The little paste window is popping up but it still wont let me paste….

[HopperParticipant @hopper]

Might this be an instance where CNC is the best way to go? There have been plenty of standard lathes fitted with "digital leadscrews" using CNC gear to move the carriage along in relation to the main spindle to form a precision thread. Sure it's been covered in MEW some years back. All this application would need would be to make the thread a coarser pitch. Presumably just a matter of programming in the right numbers? And you would not run into the problems with very large gears not fitting the banjo and very high gear ratios straining the little plastic gears of a mini lathe.

Just a thought.(From someone who knows nothing much about CNC.)

[Michael GilliganParticipant @michaelgilligan61133]

Posted by john constable on 20/06/2018 23:06:52:

I'm having trouble posting a jpeg. The little paste window is popping up but it still wont let me paste….

.

Sit quietly with your beverage of choice, and read this: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=103028&p=1

MichaelG.

[JasonBModerator @jasonb]

Posted by john constable on 20/06/2018 22:53:39:

Posted by JasonB on 20/06/2018 21:10:14:

Posted by john constable on 20/06/2018 20:17:44:

. What would it take to get a lower pitch?

do you mean a higher pitch where the pen moves along the work even more,

yes higher pitch – less thread-like. someone mentioned that you could reverse the wheels on the banjo to go higher.

That is what I did for the video, quickly swapped the fine feed gears the opposite way round, had I spent a bit more time I could have got about 40mm pitch but no more with the supplied set of gears.

One other thought crossed my mind about using a Dremel particularly now that you have confirmed you want a slow twist and that is you will only be able to use a small 1/8" shank tool in the dremel so will have to make a number of passes with it set at different depths and also either side of the first pass to make the curved cut in a series of steps. This will require a means to move the Dremel bot sideways and in/out with reasonable accuracy which you may not get with a simple wooden carrage moved along by bits of studding.

This is what an off the shelf barley twist cutter looks like, one crest will blend into the next so the spacing or pitch between cuts is equal to the cutter diameter, you would need a good size router to hold them and make that sort of size cut.

[HopperParticipant @hopper]

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

[john constableParticipant @johnconstable10725]

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:

[john constableParticipant @johnconstable10725]

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

[Roderick JenkinsParticipant @roderickjenkins93242]

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&quot 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

[Neil WyattModerator @neilwyatt]

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.

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