Following on from my recent request for gear suppliers I thought I'd check how much gear cutters would cost (I had just assumed it wouldn't be worth buying them for a few gears). As I thought when looking at DP cutters there are about 8 cutters for each DP, depending on the number of teeth the gear has. But looking at the Chronos website they list six gear cutters, one each for mod 1 to 6. Will one cutter cut any mod1 gear regardless of number of teeth? I had thought that the only diference between mod and DP gears was the definition. But if that is the case there should be different cutters for mod1 gears depending on how many teeth they have. Could some helpful gear expert point me in the right direction here please -it seemd almost too good to be true that with one cutter I could cut a gear with any number of teeth.
Sorry not on. Just had a look at the Chronos site and their description is to vague to be understandable. The only thing they state for certain is they cover from No1 mod to number
6 mod. Module is a range, in fact its the metric version of Diametrical pitch 1mod is 25.4 DP so you can see the relation ship. 6 mod is equal to 4.2Dp which to put it bluntly is a mangle wheel. At 16mm bore there wouldn't be enough meat on a cutter that small to for a
6 mod tooth.
Looking at various scenario's I can't see what they are trying to say.
To get back to basics there are 8 cutters to a set.
CUTTER NUMBER 1 . WILL CUT 135 - RACK CUTTER NUMBER 2 . 55T-134 CUTTER NUMBER 3 . 35T-54T CUTTER NUMBER 4 . 26T-34T CUTTER NUMBER 5 . 21T-25T CUTTER NUMBER 6 . 17T-20T CUTTER NUMBER 7 . 14T.16T CUTTER NUMBER 8 . 12T-13
Looking at this you will see that most users will probably be able to get away with just the central 3 or 4 instead of a full set, depending on what they want to do.
A decent site , with prices is RDG's
They have a page of reasonably priced gear cutters. Ignore their cut and paste description that has every range of cutters being suitable for Myford gears, that only applies to 20 DP.
The catalogue I was referring to above was the web page. Just got a printed catalogue and on page 50 it seems to indicate sets ( at from £79 to £85 each inc VAT and shipping) from 48DP to 12DP with 1" bore and from 1mod to 6 mod with 27mm bore. these are at 20deg PA but ask for other sizes and 14.5PA. single cutters can be ordered by appending the cutter number to the part number for the set.
Just had a look in my printed catalogue -never thought of looking there as I asumed the web site would be more up to date, obviously not the case.
From the way I read it, those prices are per cutter (ouch!), which does seem about right when compared to the prices of the other cutters on that page. I think I'll stick to HPC for odd gears. If I ever need to cut some there have been several articles in Model Enginer on how to make gear cutters like these. I thought it seemed a little long winded, but at these prices it seems moe worthwhile.
Just a thought, there must be a fair number of cutters in each of our stocks, why not set up a sharing system? I know that I have about 20 or so of various sorts and would be happy to lend them for free, the person borrowing to pay recorded delivery postage both ways and promise to replace if damaged in use. That equates to less than £4 per cutter, cheaper if more than one is posted.
I am sure the more reliable members of the ng could be trusted not to take advantage.
-- Peter A Forbes Prepair Ltd, Luton, UK firstname.lastname@example.org
RDG are doing 14.5 PA cutters at a very reasonable price. All UK makers lathes other than possibly late model Colchester's which moved onto module are 14.5 PA which is probably what most people want them for.
I'm ashamed to say that I got a set of 16DP cutters from them. They are HSS and labeled GARVIN. They come in a traditional cheap wooden box. I have a sneaking suspicion that the Dickenson brothers and Chronos are getting their stock from the same place since the prices are very similar. Had I known I could have got them in 20PA from Chronos at the time I would have got those. As it is, I'll just weld up all the teeth in the gears and re-cut the lot.
I spent the last weekend and a half making a mandrel to use the cutters on. I started with a bit of ex agricultural machinery shaft 1.25" in diameter and
The first step was to bore one end out to 22mm to fit a blank MT2 arbour. I centred one end in the 4 jaw chuck and drilled a centre drill hole in the far end. I then turned a bit of the surface to give a clean journal to use for the fixed steady when boring. This did not go well. The steel is a fairly high carbon steel and hardened. It machined but left a torn and ragged finish.
I did not want to fully anneal the bar because I felt that it would do a better job in its heat treated condition. The obvious solution was grinding. I didn't have a toolpost grinder so I made do with a slipstone in the toolpost. I used a rotating centre for support, an emulsion of meths and white spirit as coolant and lubricant and ran the lathe as fast as it would go. After a couple of hours I ended up with a one inch length of surface with a mirror finish. I could then mount the fixed steady (note to self... leave some of the machining marks on the steel, they help to hold the oil). After that, drilling and boring for the blank arbour was trivial.
Having press fitted the blank MT2 arbour in the end of the mandrel I mounted up the vertical slide and milled a 1/4" keyway in the area of the mandrel that was to take the gear cutters. Then mounted the MT2 end in the lathe mandrel and drilled a centre hole in the other end.
After some experimentation I discovered that I _could_ get a good surface finish on this steel. all that it needed was a cut of greater than 25 thou, slightly negative rake and a surface speed of more than 300fpm The swarf comes off grey rather than blue and burs if it bundles together too tightly. This is on a Myford fer gossake! The downside of this discovery is that there was a keyway at the end of the cut. keyways are not good for carbide inserts at
A few hours work with the shaper and some welded together bits of 3"x4"x3/8" angle iron scraps lead to a bracket that could mount a cheap and nasty bench grinder to the back of the cross-slide. now we're cooking with charcoal.
Another note to self... 5 thou is more than enough for grinding. 25thou is silly unless you've got the whole,day to waste. I used 7 thou to clean off the machining marks and adjust out 2 thou of offset from the tailstock and the rest was hogged off 2 thou at a time.
By 20:30 tonight I had the mandrel finished. 16" long plus MT2 shank with 11" ground to 0.9995" +- .00025". Not bad for a 54 year old ML7.
This week I'll put a 5/8"BSW thread on the end of the mandrel, shape up a 1/4" key and make some sleeves with keyways to go over it. Next week I might be able to try out the gear cutters :-)
The opinion on the gear cutters so far is that their fit on my mandrel seems to vary between quite easy and "must-use-oil-and-screw-the cutter-on-to-stop-it-binding"