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View Full Version : Gearcutting newbie seeks straight advice...



Davek0974
08-26-2009, 07:56 AM
Hi all,

I have done plenty of machining before but never gut a gear and find myself needing to make several large gears in cast iron with 4DP involute teeth, 14-1/2 pressure angle.

Its for a traction engine I'm building. I have just got hold of a horizontal mill, an Adcock & Shipley 2E with 40int taper and 1" arbors. I have the gear cutters, all 3.625" dia with 10 or 12 teeth depending on number. I have studied books, formulas, dividing and so on and am confident that i have enough basic knowledge now.

The reason i am posting is to try and clear up the massively conflicting advice i have been given so far regarding how to actually make a cut. Some say go full depth in one pass at x rpm, others say go at minimum rpm and make several passes per tooth, yet others have said pre-gash the wheels with a plain cutter first or start slowly and work upwards (but upwards to what?) and so on.

I know i may have asked these questions here before but only as part of another topic and did not get a straight answer. As it is for home shop use, cutter life is the most important factor and as long as it gets done in a reasonable time frame, speed is not too important. The largest wheel has 77 teeth.

Can anyone suggest a good, sound base to jump from regarding DOC, speed etc????

Any help really would be much appreciated.

Thanks
Dave

J Tiers
08-26-2009, 08:35 AM
I have not cut such large teeth.

However, I belong to the "gash first" group. if you want cutter life, you get the job done with the fewest cuts that you can do with the expensive cutter, and the most you can with the cheap ones. Therefore, why use a finish cutter to do your roughing?

Unless you have a lot of power, it may also make no sense to try to cut full depth after roughing, unless your roughing is close to final form.

I bought a large number of cutters from a gear shop that was going out of business. Paradoxically, there were no that many gear cutters in the lot. I suspect I got the ones that were not sold elsewhere.

In any case, there were a LOT of cutters which appear to be roughing cutters, plain cutters which resembled rack cutters, (straight sides) but were narrower. They did not appear to be worm cutters, as they had sharpish corners. All of these were apparently shop-made from other things, as their stamped info didn't match their appearance.

I suspect the shop used them to rough the tooth form before finish cutting the form. A sort of "gashing" cutter that was a bit closer to final form. You might consider something like that also.

if you were not at such a distance, I could send you one that would work for your gears.

Davek0974
08-26-2009, 08:45 AM
Thanks for the offer,

I also got a serious pallet of cutters, maybe 150 of them with the mill. Mostly side/face but plenty of special grinds, maybe thats what they are too?

Due to the size of these teeth, i can probably use two cutters of differnt widths to remove a step of waste from each tooth, getting rid of metal makes sense to me.

Dave

LES A W HARRIS
08-28-2009, 01:15 AM
At 4 DP, semi-finish, then finish.

Big boys!
http://i37.photobucket.com/albums/e97/CURVIC9/09%20GEARS/VisualCADD403-76_66_55T4DP14p50PA01.jpg

Cheers,

Davek0974
08-28-2009, 03:02 AM
Ok, now i'm getting somewhere, the setup will be similar to this (not mine but the machine size and job is similar)...

http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-3b.jpg
http://web.onetel.com/~duttondock/Index/ListerJP/Flywheelgear-5b.jpg

I'm going in at about 50-60rpm and cranking at about 1"/min +, i will cut one tooth almost to depth first to use as a gauge for gashing the rest with plain cutters before fitting the form cutter.

Just got to tidy up a few loose ends now such as the best way to centre a cutter on the ring as i'll obviously need to be changing wheels between gashing and cutting?

Dave

jugs
08-29-2009, 04:34 AM
Hi Dave,
That setup is fine BUT that cutter will bounce as the arbor flexes giving incresed tool wear, poor finish & chatter marks.

Fabricate an arbor support that clamps onto the overarm as close to the cutter as pos, use a plain bronze bush, lubricated with thick oil or grease to damp out vibrations. (never use rolling bearings cos you end up with a dreadfull finish).

For best finish use a neat cutting oil (eg Castrol Ilocut 486) not soluble oil, pumped not brushed or squirted.

What traction engine are you building ?

john.

ps. before cutting metal - referb your rotary table, clean, oil/grease & adjust for min backlash. when cutting only only rotate in one direction.(I know eggs & grandma's)

good luck. john

Black_Moons
08-29-2009, 04:51 AM
a steady rest for your horzontal machine arbor. I like it. Could make something that just slaps on the bridgeport ram ways.

Davek0974
09-03-2009, 11:51 AM
Ok, thanks i'll look into possibly steadying things up a bit.

I'm cutting cast iron so no cutting fluid or suds.

Dave

Mike Burdick
09-03-2009, 12:55 PM
Dave,

Off the subject but I enjoyed your web site as well a the photos on your camera club's site. If anyone hasn't looked at them yet, the links are in Dave's signature line.