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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: spiral spindle cutter
20/06/2018 17:49:19

I was thinking I could maintain the same centre-centre distance by having more than 2 gears in the cartridge.They could be as complex as needed as they wouldn't need to be fiddled with once set up.

By two screwed rods, you mean that a chain will engage a cog on each whereas fixed cogs will only allow one?

20/06/2018 17:13:19

I'd also considered some kind of cartridge arrangement with 2 or more gears inside for a given pitch and then the cartridges can be changed for each change in pitch required and no need to fiddle with gearwheels and chains.

I couldn't quite work out how to put the cartridges on though.I'm not explaining myself very well...I can feel some sketches coming on.

20/06/2018 17:09:00
Posted by Brian G on 20/06/2018 15:59:45:
Posted by john constable on 20/06/2018 14:53:19:

.. The part I'm finding difficult at the moment is an arrangement to sync the travel of the tool along the work and the rotation of the work and do it in such a way that it can be changed easily for different pitches (in effect it's some kind of simple gear box needed).

Going back to my Heath Robinson lash up, how about using a leadscrew (from DIY store studding) connected to the spindle by Delrin chain like this? **LINK** You could get 6:1 reduction with 8 and 48 tooth sprockets, so two pairs would give you 36:1 and a 36mm pitch using M6 studding for the leadscrew. Unlike gears, it would be easy to accomodate the spindle-leadscrew distance and a third wheel acting as a movable tensioner could adjust the chain when you changed sprockets.

Meccano chain and sprockets would be a little more sturdy, but only offer 4:1 reduction, although it would be simple to combine this with gears and would allow a massive range of spiral pitches.

Brian

Thanks, Brian. That looks like the best type of hardware to use. I never came across Delrin before. I wanted to use meccano but as you say the choices are limited although someone mentioned a robotics supply site.

How would you arrange the gears for different ratios? Would you use a pair for each different pitch you wanted and then just connect your chain to whichever you needed for each job? How would a moveable tensioner work? Would it need to move in a slot to take up the slack and then be held there with a nut or something?

20/06/2018 14:53:19

Yes - essentially you're all correct. I had a trend router lathe but it was lost in a house move before I could use it and I had to stop woodworking for a while so I didn't replace it.

More recently I've ended up in a wheelchair with mobility problems and a full sized set-up is beyond me to use so I decided to put together a miniature workshop and concentrate on small decorative things like boxes and clocks - hence my desire to make barley twists from maximum 2" x 8" stock but usually smaller.

The trend router lathe will be too large for me and also I think not accurate for the scale I want to work at.

There are two routes that seem to have opened up to me. Firstly getting a mini lathe which has change wheels and a disconnectable motor. That's not cheap but on the other hand offers me the joy of other things a lathe can do.

Or home-made,like Brian's sketch. That's similar to the pen wizard but I don't want to use cords because I think they'll be inaccurate. The part I'm finding difficult at the moment is an arrangement to sync the travel of the tool along the work and the rotation of the work and do it in such a way that it can be changed easily for different pitches (in effect it's some kind of simple gear box needed).

Thread: Chinese mini-lathe change wheels
20/06/2018 01:08:57

That looks really good.Read other posts on it vs the SC2. Sadly a bit outside my budget.

20/06/2018 00:24:27

I'm wanting to barley twists and spirals in wood stock up to about 2" x 8" max. Someone has explained to me I need a small metalworking lathe with change gears so I can radically speed up the saddle to spindle speed and turn the spindle slowly by hand.

I noticed you guys discussing small lathes and change wheels. Could you suggest any new or used mini lathes with change wheels that might fit the bill please?

Thread: spiral spindle cutter
19/06/2018 18:29:20
Posted by Keith Long on 19/06/2018 18:01:42:

Hi John

No you don't need a motor on the lathe, in fact for what you what to do you don't WANT a motor on the lathe, things would happen at frightening speed! With the way the gearing would work turning the hand wheel on the end of the lead-screw will turn the main spindle as well quite easily.

The hand wheel on the slide (aka saddle) will move the saddle along the lathe bed but not under control of the lead screw. That hand wheel shaft has a gear on the far end which engages with a rack mounted on the lathe bed, if you look carefully you should be able to make out the teeth on the rack behind the lead screw. For your purposes you'll want the engage the half nuts onto the lead screw - operated on the lathe shown by the lever sticking up at approx 30degs. on the left side of the saddle. That will engage the saddle with the lead screw which will then control the movement along the bed.

If you're thinking of the Unimat with the twin parallel round bars for the bed - don't bother, it used an entirely different means of thread cutting which isn't suitable for your requirements and would require a lot of fiddling to make it work for you. Also as you've noticed they tend to go for gold plated prices generally.

Thanks, Keith. The unimats certainly are pricey. You're explanations are bringing my 35 year old engineering lessons flooding back to me....

So, the good news is I might even be able to save some money by finding something without a motor...

19/06/2018 17:41:41
Posted by Keith Long on 19/06/2018 15:04:31:

John - have a look at the following webpage (http://www.lathes.co.uk/winfield/index.html). This is a simple (old) screw-cutting lathe. Along the front you can see the lead-screw with a hand-wheel on the right hand end and a set of gears at the left hand (headstock) end. Those gears are mounted on a slotted bracket, usually called the "banjo". The gears are located on the bracket by short axles that can be moved along the slots to accept the different size gears. The gears connect the lead-screw to the main spindle and you can change the gears around - or use additional ones to get (within reason) whatever gear ratio you like between the main spindle and lead-screw, that's how you set up to cut different screw thread pitches. Normally for cutting screw threads the gearing will be such that there is a reduction in speed between the main spindle and the lead screw. For your application you'll be looking for a speed increase from the main spindle to the lead screw so you'd assemble the appropriate gear train basically the "other way round" so that the small gear was on the end of the lead screw and the large gear on the end of the spindle. You'll see in the picture 4th from bottom of that page that the gear train isn't just a "simple" train but is a compound train - 2 gears rotating on the same axle and locked together, each connected to further gears in the train - that's how you get the flexibility in the ratios.

I'm not suggesting that the lathe on that page is the one you should look for - although it would do the job you want perfectly well, but picked up that page a showing a typical older style screw-cutting lathe so that you could see how the gearing is arranged. There are many lathes of that type knocking around and they can often be picked up quite cheaply. If you can find one with a good set of gears (change wheels) the so much the better, but gears can be adapted and modified as needed, the trick is to try and make sure that the gears that you want are a common pitch (tooth spacing) as that will mean that they are more readily available and usually cheaper. The bore of the gears can either be machined out or bushed down to suit and key-ways are pretty easy to cut (for one or two) with basic tools. Some lathes used pin drive into the face of the gear in which case you just need to drill a hole in the right place.

If you do go down the old lathe route don't be tempted by one with a screw-cutting gear box, the gear train will be completely wrong for your application and a nightmare (if even possible) to convert.

Keith - this is brilliant stuff, thanks. I've been browsing ebay and google looking for helical milling machines over the last couple of hours because that seemed the most descriptive term for what I was looking for. I ran across some old lathes with interesting looking gear arrangements, including the unimats, and I was going to come back with some more questions which you have preempted.

Do I need too use the motor or can I turn the spindle by hand? I'd prefer the extra control and overrunning the cut would not be good!

Can I ask the difference between the wheel on the tailstock end of the leadscrew and the large wheel on the slide? Dont they both turn the leadscrew and move the slide?

I thought the unimat might be suitable as there seems to be a lot of options for it which may well include these gears but they look a bit pricey. Could anyone suggest some suitable models to me please? Not too large if possible as I still only need to turn things less than a foot by 2".

19/06/2018 14:54:03

I understand I'd need to change the gear ratio but I'm not sure how to do it without reconstructing it every time. I could add more gear pairs with different ratios and move the chain each time but its still only one pitch per ratio and i'm not sure how I would change the chain each time if there's no slack in the system.

19/06/2018 14:18:30
Posted by JasonB on 19/06/2018 13:32:20:

It can be done on the mini lathe.

-Make a bracket to hold Dremel or router on the cross slide where the cutting tool would normally go.

- Make something to hold a large gear/pulley etc on the far end of the main spindle

- Make or possibly use the existing gear position on the end of the lead screw to hold the smaller pinion that will drive the large spindle gear. The leadscrew is the long screw that runs along the front of the lathe.

- Make a handle to turn the leadscrew with, this could just be a ply or MDF arm with a knob to get hold of.

- Set the Dremel running, use the cross slide to move it into the work and then turn your leadscrew handle which will make the Dremel move along the work as it slowly rotates.

EDIT this guy did a 1 turn per inch spiral using the supplied gears by setting them in teh right order, may be possible to get a steeper spiral that way.

Edited By JasonB on 19/06/2018 13:37:16

Thanks for that video. I think I see whats going on now. The problem this guy has ended up with is one I'm grappling with. How do you vary the gear ratio for different pitches? At least he's managed a low enough pitch to get one working. I didn't think that was possible on a small hobby lathe.

19/06/2018 14:08:14
Posted by Keith Long on 19/06/2018 13:42:50:

As Jason says above, it can be done on a lathe - easier than messing around with a mill and dividing head etc.

Assuming that you haven't got a lathe or milling table etc yet, keep a look out for an old simple lathe that has screw cutting abilities, ie one where you can gear the lead screw to the main spindle. For your usage you probably won't be too worried about the state of the bearings on the main spindle - so long as the spindle isn't flopping around everywhere, you won't need the sort of rigidity and precision that metal turning would. The issue to solve then is getting the gear train to connect the lead screw to the main spindle and here you needn't stick to the "correct" gears so long as you can construct a working gear train. Gears can be bought from EBay as well as dealers, but for your usage gears from the like of Technobots would also be suitable.

If you haven't got access to metal working machinery (a lathe) for making the odd bits that you'll need, give us a clue to whereabouts in the country you are, the chances are that there wi8ll be someone near to you who would the able and willing to help you.

Thanks, Keith... I feel I’m getting closer all the time.

I think which ever method I’ve looked at it’s the issue of driving the lead screw from the spindle that is the trickiest part. At it’s simplest I imagine a cog on the spindle and a cog on the lead screw in line with it and a chain joining the two?

Assuming I can choose cogs that give me the right speed ratio for a barley twist pitch, how do I vary it to vary the spiral pitches or would I just be stuck with one?

If thread cutting lathes had a bigger range of ratios we might be in business!

19/06/2018 13:53:47

I'm doing my best to picture that. I'm ok with mounting the dremel to the crossslide somehow.

The lead screw is the long threaded rod that is motor-driven to move the carriage along the length of the lathe. Presumably it can be disconnected from the drive and you are proposing I turn it by adding a knob on the end? If its what I think it is, dont most lathes have a wheel for manually turning the lead screw already?

19/06/2018 13:01:21

Wow... I wish I understood what you are all saying!

What I do pick up from it is that what I need is model/hobby sized helical milling machine?

I suspect they dont make them.... so how do I create one? Can a mini metalworking lathe be modified? In my original post I outlined how I thought I might go about making one from scratch. I just need a way to link the hand-turned chuck with the milling table wheel in such a way I can control the spiral pitch. A simple gearbox I suppose or an arrangement of cogs and chain like you'd have on an old lathe to control speed. That much eludes me.

So frustrating a metalworking lathe just can't quite do it!

18/06/2018 23:13:28

thought I'd post these for your interest.

Ive listed them in reverse so you can see the results first then how he built it.

I wonder if you can get tiny bikes complete with gears?

https://www.youtube.com/watch?v=v1kpXPzYhoM

https://www.youtube.com/watch?annotation_id=annotation_2902547835&feature=iv&src_vid=v1kpXPzYhoM&v=2eDaGgi1lpQ

18/06/2018 23:05:29
Posted by Michael Gilligan on 18/06/2018 21:33:03:

John,

I've just been browsing around, and found this page: **LINK**

https://stusshed.com/tag/beall/

The first couple of pictures are another [perhaps the original?] routerlathe-style device ... but then it gets more interesting: Maybe sufficient to get your inventive streak going.

MichaelG.

.

Edit: Here is Beall's website:

**LINK**

Where you will find detailed instructions and some excellent photographs angel

Edited By Michael Gilligan on 18/06/2018 21:41:20

Fantastic! You star! A bit worried it'll only do pen-barrel size stock but maybe I can stretch it. Holding stock will need some though because pen barrel blanks are hollow and held in a mandrel.

Not cheap but it looks worth the money and probably cheaper than building my own from scratch.

Thanks, Michael.

18/06/2018 20:51:31
Posted by larry phelan 1 on 18/06/2018 20:34:20:

Hi John,

I have an old Trend catalog buried deep [not seen it for years],in which the is a machine,using a router to do just that kind of work. The router is arranged to move along the workpiece while the work revolves. The speed of the advance is dictated by a wheel,turned by hand.

Might be worth checking out Trend

That's the trend router lathe that the guys have pointed me towards. Its quite a complex arrangement of runners, pulleys and strings. I think it would be hard to make one from the few pics available but I dont think it would be suitable in a smaller form for the size of work i need.

18/06/2018 20:46:41

I think I see what you mean. So it's basically what I was proposing but instead of turning the chuck by hand I'd turn the table advance knob by hand? Either way the tool would still be static in the drill stand.

Would some kind of flexible shaft be a mad idea? Too much play?

18/06/2018 20:30:03

Believe it or not I had a TRL but it got lost in a house move before I had the chance to use it and I never had the opportunity to replace it.

If dremel made one that would be great but that arrangement of strings and pullys looks harder for me to achieve than using a couple of cogs and a chain - especially on the scale I need to work at.

18/06/2018 19:15:48

High everyone! New member, first post and first project!

I want to cut spirals on spindles (aka barley twists) in wood and it looks like its going to need a custom tool.

It's basically as 'simple' as replacing a lathe tool with a router and getting the work to rotate slowly in sync with the tool moving along the bed and not at a cutting speed. Hope that makes sense.

All of this is just for miniature work on spindles up to 1.5" thick and up to 6" long so a full sized lathe is overkill.

A metal work lathe that can cut threads will sync rotation and tool travel but I can't see how you would get the work to rotate slowly enough, the pitches seem to be too small and from what I can see see I couldn't justify such a large cost. A smaller one would be cheaper but would it cut threads and support a dremel?

Having set metalworking lathes to one side, I looked at woodworking lathes. On full sized older and cheaper lathes you can disconnect the belt drive and turn the work by hand but you can't sysnc tool movement to rotation. Smaller lathes have a direct drive motor which wont turn slowly with any kind of torque but there's still no easy way of syncing them.

My current plan is to bolt a milling table onto a drill stand with a dremel in it and fabricate a headstock and tailstock to hold the work. Then I can turn the headstock (large chuck?) by hand and link the rotation of the headstock using a sprocket and chain arrangement to the bed advancing wheel to move the work under the tool.

So, I'm really looking for ideas - alternative ideas that might fit my skills and budget to achieve my desired result or just where to get suitable sprocketage and chainage from.


A couple of other thoughts - the pitch of the spiral is in the order of 1:1 (that's the diameter of the spindle in tool movement versus number of rotations) but of course I really need to vary that slightly to increase and decrease the spiral pitch. And I looked at a stepper motor solution but its an area i'm unfamiliar with and I know its going to involve controllers, iterfaces, pcs and software etc so I dont think it would be an easy or inexpensive path for me .

Any advice offered gratefully received!

Thread: Hi from Bagshot
18/06/2018 17:33:12

Hi everyone.

I used to enjoy woodworking decades ago but life got in the way and I couldnt keep it up. More recently I became ill and ended up in a wheelchair with more time on my hands so I decided to set up my workshop again only this time in miniature, using dremel-type tools and making small ornamental items like clocks.

So, I realise this isn't a woodworking forum but there's one thing I want to achieve - decorative spiral cutting - that's going to need a home-made tool and that's why I joined this forum. But I expect to pick up a lot more really interesting things along the way!

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