Press/shrink fit Bronze?

CJD · Nov 27, 2019

I need to make a set of double gears, module 1.5 with 22 and 24 teeth. Since they are adjacent each other, the smaller gear cannot be cut without also cutting into the larger gear. I plan to cut them separately, having a shaft on the smaller so that the second one can be pressed onto it.

The originals are steel, but I would prefer to use bronze. I just wanted to check and make sure that bronze will not be too brittle to shrink or press fit together. If it is, I will make them in the original material.

Their use is as the lead screw selector gears on a lathe, so only moderate loads against other well worn gears (thus my preference for bronze).

FredC · Nov 27, 2019

Another solution could be to Loctite the bonze in. With a precision slip fit then Loctite you do not get the distortion and shaving that happens with a heavy press fit.

Russ115 · Nov 27, 2019

Bronze will press fit just fine. You might need to ream the center after press fitting. Silver solder works nice on bronze also and doesn't require much clearance to flow, and would probably be stronger than the gear teeth.

CJD · Nov 28, 2019

Thanks guys...good tips.

ss_user · Nov 28, 2019

I'm partial to shrink fits rather than press. Of course that really means you need the shaft out of the machine. ;-)
The coeff of thermal expansion for bronzes (tin bronzes) which seem to be recommended for gears is about 50% higher that steel which make shrink fits easy. Cool shaft in dry ice and warm gear in oven. I've did this on a ball bearing only I couldn't warm the seat, just cooled the bearing, it slipped in and in seconds it was there to stay. Make certain you are rigged to slip it in place accurately because once it cools down is it quite solidly affixed. YMMV

CJD · Dec 2, 2019

Thanks! Shrink fit it will be.

I'd have this job done, but I have been playing musical chairs with ordering the cutter. The first order took 4 weeks to get the wrong cutter from China. Now I have been waiting over a week for one ordered here in the States, but after a week they just let me know they are "processing" the order. An entire week just to start processing a single item order. I hate trying to accomplish anything during the holiday season.

ss_user · Dec 2, 2019

The holiday season is a bad time to be in a rush. Employees take time off. Stuff goes missing or gets rerouted in shipment.
Hope your cutter situation resolves itself.

ss_user · Dec 2, 2019

The holiday season is a bad time to be in a rush. Employees take time off. Stuff goes missing or gets rerouted in shipment.
Hope your cutter situation resolves itself.

CJD · Dec 4, 2019

Thanks...

I watched a video on machining a gear hob from tool steel. If I have any more trouble getting the cutters I may give that a try.

CJD · Dec 12, 2019

Finally got the Module 1.5 cutter. It doesn't match. The gears are so badly worn I think it throws the measurements, and therefore the calculations off. I am now starting over ordering a module 1 cutter. Cross my fingers that this time the delivery goes quicker.

This Celtic lathe is a bit of an enigma. All the settings and dials are in inches, but all the internals seem to be metric. Just hoping these lead screw gears are not bastardized mixes too...the saga continues...

johansen · Dec 12, 2019

CJD said:
Finally got the Module 1.5 cutter. It doesn't match. The gears are so badly worn I think it throws the measurements, and therefore the calculations off. I am now starting over ordering a module 1 cutter. Cross my fingers that this time the delivery goes quicker.

This Celtic lathe is a bit of an enigma. All the settings and dials are in inches, but all the internals seem to be metric. Just hoping these lead screw gears are not bastardized mixes too...the saga continues...

that's quite a shift. are you sure its not module 1.25 or could it be 20 or 18 diametrical pitch?

CJD · Dec 25, 2019

Anything is possible on this lathe. I got the module 1 cutter, and it is a very close match, but still not exact. When I run the formulae using the original diameters and teeth, it comes out to precisely module 1.5. It comes close to some of the DP cuts...but still not exact. My bet is they used a proprietary cut of their own. I plan to cut with the mod1 cutter into brass. Hopefully the brass will "wear in" to the steel gears to become perfect at some point.

Working on the arbor...then I will finally get to work.

johansen · Dec 25, 2019

CJD said:
Anything is possible on this lathe. I got the module 1 cutter, and it is a very close match, but still not exact. When I run the formulae using the original diameters and teeth, it comes out to precisely module 1.5. It comes close to some of the DP cuts...but still not exact. My bet is they used a proprietary cut of their own. I plan to cut with the mod1 cutter into brass. Hopefully the brass will "wear in" to the steel gears to become perfect at some point.

Working on the arbor...then I will finally get to work.

that is the kind of shift you would get from cutting two gears of different teeth to fit on the same center distance.

can you post a photo?

CJD · Dec 26, 2019

That is precisely the situation! These are 2 gears on a single shaft, which are selected to mate with a pair of other gears, also on their own same shaft. Could you elaborate on how the shift is determined?

cosmos_275 · Dec 26, 2019

Why don't you buy two gears and press them on a shaft? misumi GEAHB1.5-22-15-A-6 for example. They have 24 teeth as well.

CJD · Dec 27, 2019

That is an option. I think the answer lies in the challenge, though. Another issue is they are not a precise M1.5. Right now I am collecting cutters, which I will eventually use. If I were trying to match the gears, I would instead have a lot of "not quite right" gears laying around now that I would never use.

Johanson seems to have the answer, although the answer may require forming my own cutter. Or possibly cutting to Mod1, even though the calculations say it should be Mod1.5.

In any event, I almost have the arbor finished to take the cutting wheels, so I will start cutting this week if all goes well. If all doesn't...then I'll try the canned gear option. Thanks for your idea, though...as it could be the answer in the end!

johansen · Dec 27, 2019

You could try cutting the gear with mod 1 cutter, then rotate the gear a few degrees on the dividing head and cut it again.i think they call that a profile shift which would normally increase the backlash significantly. But in this case you have to do that to get the gear to mesh properly. Is this mating with a mod 1 gear?

Have you measured the gear over pins to check the pitch diameter and compare it to standard calculations?

CJD · Dec 28, 2019

I have tried ordering a set of pins twice...and both times the order sat for 4 weeks and then got cancelled. So I have not been able to measure that way. Unfortunately the gears that this little selector meshes into are all on the same long shaft that I have not removed. If I cannot hit the proper shape easily, then I will remove the other gears.

Today I studied the cutters compared to the original gears carefully, and the mod 1 cutter looks very, very close. It will cut the teeth just a couple thousandths "fatter" than the originals...but considering the original gear is totally worn out, this may be the mod used at the factory.

I think you are saying that a module "shift" is just a matter of opening up the space between the teeth just a bit...obviously to allow for a slight mis-match with some of the 15 selector gears that must be mated to it? If so, that would be a very easy thing to do. I could even cut exact mod 1 initially, and see how it meshes, and then re-cut a bit more "open" if needed.

Well...enough talking. I finished the arbor yesterday, so today I take a stab at the gears. Thanks again for the help, Johanson.

CJD · Dec 30, 2019

OK...a close out for this thread. I finally decided the mod 1 with a lighter than usual cut was the ticket. Here is the setup on a practice run:

Notice the cut is too deep. This run was to practice with the G code and depths. Everything went great, with the hardest part being learning the HSM for wrapping the cut around the gear. The cuts went like butter...the only issue being when the job finished the HSM G code sent my spindle careening through my rotary table! I didn't get the press/shrink as tight as I hoped, so I used solder...as recommended by Russ above...to seal the deal. In the end the gears have .005 back lash...I couldn't hope for a better mesh for an unknown module. So the lathe is back in operation!

One thing, Russ, i practiced a little silver solder, but was afraid the melting point was too close to that of the Bronze. I chickened out and used low temp, as the time to re-cut outweighed the risk of failure. I may try again on a less critical part sometime.

Thanks again to all who provided tips!

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