SPG Tools

Ok, it's definitely a helical gear, or at least masquerading as one. The helix angle will be small, as it should match the worm. Even if cut straight across at an angle, rather than the true helix, it should be ok.

Ignoring the helix angle it seems to be a 1Mod gear, which gives a circular pitch of 3.14159 etc. The pitch of the worm should be the same, ie, irrational. I wonder if they've fudged it to mate with a worm with a 3mm pitch?

The teeth are worn off centre and only on the tops of the teeth. So I agree with Michael that the meshing is wrong. Whether this is because the alignment of the gear housing is wrong, or gears with different circular pitches are being forced into mesh is a moot point. Either way it's a mess; where's Oliver Hardy when you need him?

Andrew

PS: Well I never, it seems I share a birthday with Oliver Hardy

I think the whole fine feed thing is a joke, i think the whole problem stems from a mixture of things starting with back lash on the rack and pinion on the main column. The fine feed when it does engage has to turn several times just to get the backlash out before it actually fine feeds in one direction and often the whole head drops around a mm or two and then you have to turn it multiple turns to get it back where you want it.

i`ll have to think what im going to do to fix it so it works a bit better.

Also i suspect that these mechanisms later were later changed somewhat as there are parts of the fine feed rod that appear on the parts diagram i got from a advertiser on here that certainly arent on mine such as the fine feed rod which on mine is just a plain rod but in the brochure it is different and more similar to the seig mini mill variation.Such as part 138 (adjustable union)

Edited By mark smith 20 on 31/10/2017 16:47:49

Edited By mark smith 20 on 31/10/2017 16:49:43

Edited By mark smith 20 on 31/10/2017 16:51:49

Hi Mark,

Is your worm pinned to the shaft like the diagram? Have you checked that it hasn't sheared?

Steve.

Hi Steve it may be but i dont think its sheared ,it certainly wont turn . The bits in the middle of the long bar are certainly not the same as mine despite being it the manual.Mines just a straight long bar with the worm possibly pinned on one end and the handwheel/dial on the other fixed on with a socket head grub screw..

Although this started as and SPG thread it is probably fair to say many of the similar offerings by other importers are likely to be the same and there may be some suffering Friday-fit variation in quality.

This whole mechanism concept is standard for moving quill mill/drill functions right up to a Bridgeport probably with inevitable drawbacks from the mixture of worm and rack suffering in the hobby models from cost saving> poor engagement>jerky movement.
If you want a precision down feed add a proper leadscrew at the side. Otherwise longer term you might need to look at adjusting the rack>pinion depthing as well as the worm>wheel depth when you fit a proper wormwheel.

My earlier suggestion was a 'get you home' especially for beginners who perhaps got the mill second hand and already worn and while not an optimisation of the design is no worse than as original so should last long enough to learn worm wheel cutting.

Why not lengthen the hole in the block so you can get better mesh?

Leave it in the worn alignment, it's gradually turning the gear into a proper worm wheel...

Neil

Looks like others have had similar problems with fine feed not working  with the same mill on here before. notice the same shaft with none of the linkages in the middle like the on the parts  diagram .

**LINK**

Edited By mark smith 20 on 31/10/2017 18:06:01

Edited By mark smith 20 on 31/10/2017 18:07:47

Coming in late, as usual, presumably the normal up and down movement via the handle still work?

Otherwise the problem may not be the worm and wheel, but somewhere in the Rack and Pinion area.

Howard

The mill now comes with the pulley and belt conversion at least the one I bought earlier this year did.

I found the only way I could get round the backlash causing dig ins was to ensure that you kept pressure on the handle while adjusting the fine feed down. I have bought and installed the dro system that he sells. Seem to be fairly accurate, at least as accurate as thr mill will allow it.

I am managing to work down to hundredths of a mm with care and patience and sharp tools.

Roger