How should I measure and specify gears to be made up?

[Eric The Viking]

I'm working on a small tablesaw "restoration" with a friend on the forum (two saws actually, of very similar but not identical design).

To get around an annoying design 'feature' on one saw, we're looking at an alternative arrangement, but it will involve a new pinion gear/handwheel being made up to mesh with a quadrant 'rack' (it adjusts the blade's tilt).

We have both the rack and the existing "pinion" gear intact-ish, but one important reason for the change is that the pinion is plastic (I think glass-filled), whilst the rack is steel, so the pinion is unlikely to survive long if put back into service as-is.

Here is a rough idea of what we need, badly drawn-up in Sketchup:

It's basically a knurled handwheel that can slip over a 10mm shaft. It rotates on the shaft, but doesn't grip it at all.

There's nothing critical about how the gear is machined - the clean shoulder that I've shown isn't very important (we can position the wheel on the shaft against a grub-screw-locked collar if necessary, or even a lot of washers!). The thing could even be made in several pieces, although I can't quickly think of how we might hold them together later on.

The shaft itself does the rise+fall of the blade. We intend to reduce the thickness of the main blade height adjusting handwheel (it presently has the cog and slides along the shaft to engage for tilt adjustment). This new handwheel will slip in behind it so that the two can be turned independently. This should be both longer-lived and easier to operate precisely.

At a guess the knurled part probably needs to be about 60-70mm diameter, and the tip-to-tip diameter of the cog is 20mm roughly (12 teeth). It's probably best made in steel, but brass or even aluminium would probably serve well - there's little force exerted on the teeth as it's only tilting the saw blade and motor against gravity, and it carries no continuous load as the tilt is locked off in use by a separate clamp. I have yet to determine the thicknesses of the various parts of the new wheel - probably 6-8mm for the knurled bit, with the cog part similar, and the central "spacer" part to suit.

Any advice on places on the net to learn from will be followed up enthusiastically!

Thanks for advice,

E.

PS: It occurs to me that 3D printing might be possible, however I'd have to get from SU into a suitable format (with a good model!) and it might also be too expensive!

 

[Droogs]

Have a read through this Eric:
http://www.slideshare.net/Nuumero1/metr ... rferometry

or DL this PDF:
https://www.google.co.uk/url?sa=t&rct=j ... 7w&cad=rja

 

[AES]

@ETV:

Eric, those 2 links from Droogs are very good but if you want a more "direct"/less theoretical approach I would recommend Mathias Wandel's site. Although he makes most of his gears in wood, his program (which you can either buy or use direct on line) applies to gears made of any metals too.

Link: "Woodworking for engineers" - http://woodgears.ca
then look for his gears pages.

HTH

AES

 

[Cheshirechappie]

HPC Gears may be able to supply a couple of pinions off the shelf - http://www.hpcgears.com/pdf_c33/23.114-23.119.pdf

To check whether you've got the right size of tooth, measure the outside diameter of the gear the pinion is to mesh with, then count the number of teeth and add 2. Divide (number of teeth +2) by OD in inches, and you'll get the Diametral Pitch (DP). Select the appropriate DP chart from HPC Gears' Spur Gears, Imperial, page, look down for the number of teeth you want on the pinion, and read across for the price for either bossed or plain gears. (12 teeth at 3/4" OD is very close to 18DP, so that's the page I've linked to.)

You may have to do some machining to open out the central bore, and make the handwheel, but they're relatively easy compared to machining a gearwheel.

 

[Wildman]

if you are making the rack and pinion then sizes can be chosen however if you have one but need the other be aware some gears are measured in Circular pitch and some in Diametral pitch you need to know which is which.
By the way is that just a stock ger you have added or one you have drawn, if drawn what addon do you use to draw them. (I assume you are using sketchup