Hobbymat tumbler gear instructions

Hi,

Some time ago I picked up a "tumbler gear" (screwcutting reversing gear) kit for my Hobbymat MD65. Unfortunately in the time between "receiving the tumbler" and "receiving everything else I need to refurbish the lathe", the instructions have gone missing!

Does anyone happen to have a copy they could scan or photocopy for me?

I've put some photos of the gear assembly here: https://imgur.com/a/3RsrPxG
I have a poor photo of the first half of the first page of instructions from the ebay listing, but that's it - no installation instructions or cutting guide for the gearbox cover

Thanks,
Phil.

Phil,

Did you locate any instructions or have you figured it out?

Peter

Hi Peter,

Sadly not. I found a copy of the installation instructions but sadly the change gear list and diagram are unreadable. The gear list seems to be different to the one on the machine.

Cheers,

Phil

Phil,

Any chance of a copy of what you did find?

I was given one of these lathes, which I believe was acquired 2nd hand from Essel in 2001, that has been modified with the addition of two extra motors. One a Parvalux with a right angle reduction box is fitted with an elephants foot. On the back of the dog clutch is a face plate with an "O" ring. If the power feed lever is pushed to the right the elephant foot drives the face plate via the "o" ring "clutch plate". There is an extra brass sleeve over the clutch lever pillar that engages with a switch so that as well as connecting the drive a switch is made and power feed to the motor. However with all this fitted changing the leadscrew change wheel is a bigger deal.

I have the following changewheels, 20,30,35,40,50,55,60,65,70,75 & 100. I have also rewritten a BASIC programme to look for other and more accurate combinations. I have 3D printed in ABS a further gear of 63.

Whilst the Parvalux motor is an elegant solution was looking at the tumbler as a simpler solution.

Peter

I have a Hobbymat fitted with the tumbler reverse so I can supply pictures and measurements if this is of any help.

Roger,

Pictures and measurements would be very useful please.

Peter

I have put some pictures in an album called Hobbymat. The reverser was fitted to the lathe when I bought it. It appears to offer a reversible fine feed but for screwcutting I have always gone back to the original pieces.

If this is what you have I am happy to dismantle things and take more pictures/measurements.

Roger,

Thanks, has cleared up that it is either/or and not both. I can understand going back to the original for SC, since it not actually a screw cutting reversing mechanism, which was mentioned as, at the top of thread. I have started to draught the layout in CAD and should be able to calculate the dimensions.

Peter

Hi Peter and Roger,

I've uploaded the two images I have into an album. Unfortunately there's a page missing but after some cleanup they're mostly readable.

Thank you

Thank you

Hello all.

I have joined this site with intrest in the topic of this thread, the reversing tumbler gear attachment.

There are several people who would like to duplicate this for their latyhe but lack drawings to do so.

Would anyone be willing to provide detailed drawings/measurements for us to do so?

Thanks in advance.

For the purposes of threading what the tumbler gears do is effectively make it easy to add an extra idler gear in to the gear train then revert to normal RH threading afterwards. Unless you are going to be doing a lot of LH threading then reverting to RH a modification that allows you to add an idler gear into the gear train, when the odd occasion requires it, would be a simple solution. If you are planning to do a lot of feeding outwards when facing or towards the tailstock when surfacing this may be all that is required.

Martin C

Im a toolmaker by trade and would enjoy the added versatility this mod would offer. Im trying to make this small lathe as capable and easy to use as the full size machines I use regularly.

Having a gear to add or remove is not what I would prefer, Although that would be the "Simplest" thing to do, from a usability standpoint this would get tiresome.

Thanks for the input though.

Did anyone provide the drawing of the tumbler revers, please ?

Sadly I haven't got a drawing but I do have the (unfitted) tumbler mechanism and could take measurements or scans if that'd help. My measuring instruments are limited - I have a micrometer, a set of digital calipers, a Mitutoyo DTI and the usual rulers and so on. No fancy kit like surface plates, sadly.

What I'd really like is a copy of the bits of the instructions which I'm missing - notably the gear ratios. But I expect someone smarter than I could sit down with the drawings, leadscrew pitch (I imagine someone knows that) and scans and figure things out.

If you take a look at the 2 photos I uploaded to my album, they have the two pages of the gear ratios which I have, there's another half-page of additional gear ratios I'm missing.

Of course what I really should do is put all the stuff I posted to the Hobbymat mailing list on my website - that includes a really nice cleaned-up PDF scan of the lathe manual which is very easy to read when blown up to A4 size!

Edited By Phil Pemberton on 08/08/2023 16:58:05

Once you know the pitch of the Leadscrew, (Rotate 10 turns and measure how far the Saddle moves ) should enable you to calculate the pitch of the Leadscrew.

Knowing this it should be fairly easy to work out what ratio is needed to cut a particular pitch.

You will find the contents of one or both very useful reading:

Workshop Practice Series No 3, "Screwcutting in the Lathe" by Martin Cleeve.

Crowood MetawWorking Guides "Gearing of Lathes for Screwcutting" by Brian Wood

Having said that, with a small lathe it is likely that many of the threads can be produced using Taps and Dies.

Picking numbers out of the air, for some examples, it will go something like this.

Leadscrew pitch = 1.5 mm

Required thread is 1 mm.

So Leadscrew needs to rotate at 2/3 the speed of the work in the chuck

Possible changewheel set up could be 20 Driver, Idler 60, Leadscrew 30

Could equally well be Driver 50, Idler 20, Leadscrew 75, as long as the gears all mesh correctly.

Required pitch 0.75 mm

Leadscrew needs to rotate at 1/2 of the speed of the workpiece.

so, possible set up

Driver 30, Idler 50, Leadscew 60

or Driver 20, Idler 50, Leadscrew 40

If you want a thread of the opposite hand, just insert an additional idler. Since it will not affect the overall ratio, anything that fits will fit in, say a 20 or 35.

A 63 changewheel would enable you to cut Imperial threads (With some slight, but not necessarily ruinous inaccuracies ) on a lathe with a Metric Leadscrew.

If you just want a fine power feed, how about setting up:

Driver 20, Idler 100 / 30, Leadscrew 75. That should provide a feed of 0.12 mm per rev (0.00472/rev in old money  ? Hopefully, the stud and key will be long enough to allow you to compound the 100 and 30 wheelswith a pacer to put the Leadscrew gear into correct mesh with the compound Idler.

For setting backlash, (To avoid noise and wear, no geartrain should devoid of backlash ) just run a piece of paper (About 0.75 mm ) between the gears. Start with positioning the stud to set the Leadscrew / Idler mesh and then swing the banjo to set the Idler / Driver mesh.

HTH

Howard

Phil,perhaps you can also post hte picture you have of hte unit on here to make it easier to see that going off to imgur.

The device appears only to be intended for variable feeds, not screwcutting as the spacing fixes the final gear to leadscrew at 100. The picture you have is missing the 20tooth on the stud, which has to be compounded with Z1 in the table. W is the mandrel gear.

Referring to Phil's picture (when available) it shows 4 gears of 20 tooth on a sub plate and a stud on the main plate behind coming through a slot. The sub plate pivots about the gear second from left.
The stud should have a 20 tooth gear meshing with the leftmost gear in this position. When the subplate is pivoted the left gear moves out of mesh and the rightmost gear moves into mesh. The gears are 1 module so separation is 2cm.
The pivot point gear has to mesh with a 100 tooth on the leadscrew (coming through the big hole near the bottom) so that spacing must be 5cm+1cm.
The slot in the bottom is for the clamp so measure from your own lathe.

Phil, have you had any time for this yet? I sent you and some others in the thread a PM about this.

Basic measurements for the layout would be very helpful even if not perfect, I could refine them from there and share with the group once I have it working on my machine.

Overall length, width, thickness, the pivot hole location and the pin boss locations for the gears along with the gear rack pivot location would suffice.

I will try to take some measurements of my tumbler reverse over the next couple of evenings. I don't think that there are many critical dimensions.