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Member postings for john constable

Here is a list of all the postings john constable has made in our forums. Click on a thread name to jump to the thread.

Thread: proxxon KT70 CNC ?
25/06/2018 22:18:14

OK, so I was getting comfortable with the proxxon mf70 cnc machine and adding my own controller and 4th axis. I just checked the spec and the millable area is only 7x13cm which is just a little bit too small for me. A lot of money for quite a small capacity. I'd really like a minimum of 10X20.

So, your suggestion to get a chinese overhead router is now under serious consideration....

There are loads of 3040 tables. Very few have reviews and the prices vary wildly and start around 300 quid (no good surely?) and some for several K which look very similar. There are also gantry type and pillar-drill type (some of the latter have a 4th axis).

So, please could I have your thoughts on gantry vs pillar type and can anyone recommend one or point me somewhere I can get reliable reviews?

Then there's still the self-build option, daunting as it is.

cheers guys.

25/06/2018 10:01:42
Wow. Arc kx1 is about 4.5k without software! That wont be happening be happening any time soon!
25/06/2018 09:30:22
Thanks guys I'll check those out. I was worried about spindle with the proxy on but actually it goes up to 20000 rpm which is around router speeds. I've seen several 4th axis projects for this using a rotary tabLe but I must admit preinstalled software including the 4th axis would be one less hurdle.
24/06/2018 23:08:37

If I was going to use something like the proxxon MF70 I would probably still have to mount the dremel to get the spindle speed - however, they do a 3 axis cnc kit that is pre-engineered. Then I have to add the 4th axis.

I've looked for 'gantry routers but nothing is really coming up. Are they called something specific?

24/06/2018 20:38:22

Ok - I had a massive brainstorm with a friend ealrier and it's helped to clarify my thoughts.

I've dismissed using a lathe and changing the gears. There may be cost and accuracy issues but the main thing is that changing gears may not be easy and won't give me a good range of pitches between the maximum and minimum I need - it'll only give me one discrete pitch per set up. left hand twists will be tricky.

I decided to go the multiple stepper motor route. Not only will it give me a variable choice of pitches, I'll be able to do the opposite thread and even vary the pitch DURING the cut which would be so cool. Imagine how elegant that would look!

Now I don't specifically need the lathe infrastructure, I could either custom make something or use another platform which I guess might be a milling machine that can be converted. Could anyone recommend a suitable milling machine or suggest a better platform?

24/06/2018 19:44:50
Posted by John Haine on 24/06/2018 17:02:35:

Mach 3 - you can get everything you can want and more here. It's an application that runs on a PC to control a CNC machine tool. In its standard form it outputs pulses via the parallel port that can drive stepper motor drivers directly. It is programmed either by providing it with G-code or using its internal wizards. M3 Turn however assumes that the spindle is turned in the normal way, if you drive the spindle with a stepper it becomes a "rotational axis" which is best handled with M3 Mill.

IIRC = If I Recall Correctly

Thanks, John. This doc is pretty good. It's talking about windows XP and parallel ports so I'm going to see what the more contemporary setup uses.

24/06/2018 14:54:42

someone mentioned mach 3 software for cnc control.Can anyone recommend a primer? I'd like to understand a bit more about what it is and how its used. tia

24/06/2018 14:26:31

Thanks, I'll look out for that lathe. There are some words there I need to look up.... 'making the Quorn' and 'IIRC a Potts spindle' aren't terms I'm familiar with....

24/06/2018 13:04:34
I've spoken to axminster and they're having a think.

Your right about the trend lathe. Too big and too inaccurate. I need small and accurate.

Research from that sent me to the pen wizard which looks accurate enough but it's a bit too small and offers a lot I don't really need. If they did a larger pen wizard I think I'd get one.

In terms of cutting strength as I'm using a dremel I don't think that's an issue as I'm just positioning the tool and not actually exerting any cutting effort.
24/06/2018 12:23:01
Of course I should have said that if I cen sort the gearing problem then I don't need steppers at all because as you point out, removing drive from the spindle is not a problem.
24/06/2018 12:12:42
Wow, thanks everyone. Loads to consider there. I'll have some foĺlow up questions as I work my wY through it.

May I start by answerving the question of size which was remiss of me to make clear.

Essentially i dont think im likely to want to go above 2" x 8" stock. It wiuld probably be round but of course the convenience of turn down from square would be useful.I have some mobility problems and I'm in a wheelchair with some mobility problems and I had to give up my wood working shop years ago. My solution is to rebuild it in miniature and make small decorative things like boxes and clocks so twists I make will be used in that context.

I do t just want to do bod standard spirals. I'd like to try multistart spirals almost up to straight fluting and higher pitch ones almost approaching a coarse thread. I'll also want to do hollow spirals (with deep cuts rather than drilling the core).

I like the lathe conversion route because it gives me a lathe! Providing the conversions leaves it functioning normally of course. My problems with it have been sourcing a suitable lathe without spending an arm and a leg and also solving the issue of gears. As I understand it, currently change wheels won't give me the pitches I want so I either have to change them - and I'm not sure if that's possible - or I have to drive the lead screw from another stepper motor.

What would your thoughts be on that? Is there a suitable lathe out there?

24/06/2018 00:31:28

Does anyone have experience of the proxxon KT70 CNC ready kit?

Basically, I want to make a spiral cutter and one of the options I'm looking at is adding stepper motors to a small milling table for moving the cutter (dremel) along the work and to advance it into the work and mount onto the top table a home made headstock with 3 jaw mini chuck and stepper motor to rotate it slowly.

I'm open to any information or suggestions as this world is new to me - I only heard the name Arduino 3 days ago!

Other options i'm looking at include converting a small lathe but getting the change wheel gear ratios right to get the desired spiral pitches doesn't look easy. The spindle motor would have to be disconnected too and turned by hand which is not necessarily that easy. I wouldnt mind the lathe option because then I'd have a lathe too!

However, the arduino controlled stepper motor approach looks like it'll be enjoyable to learn.

thanks, guys!

Thread: spiral spindle cutter
23/06/2018 01:30:08

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:

21/06/2018 15:11:08

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:


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....

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, 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.

20/06/2018 21:01:46

thumbs up

20/06/2018 20:25:11
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.


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

20/06/2018 20:17:44
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?

20/06/2018 20:02:26

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!

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