PDA

View Full Version : Trying to make a gear



roberlt
08-13-2005, 10:21 PM
I am attempting to make a gear using the method described by Terry Sexton in the Dec. 98 PIM.

This involves feeding a strip of .005 brass shim stock thru the tumbler gears, counting the number of teeth allowing for 1 tooth overlap , and soft soldering the ends together.

I then turned a piece of 6061-t6 to the minor diameter of the gear -.010 then putting the shim stock over the disk I filled the inside of the teeth with epoxy.

This worked great while it worked, however after a very short period of time the epoxy failed and since the teeth have departed , now left it needs dentures.

To prepare for the epoxy I cleaned everything with carburetor cleaner and then acetone.

The first try I used J-B weld and the second I used Devcon liquid steel.

Does anyone have an idea how to make this work ? Different technique, Different epoxy, ???

I am trying to use this to cut metric threads on a SBL 10K

Thanks,

Rob

J Tiers
08-13-2005, 10:34 PM
How about you do it again, and use that "gear" as an indexer to make a "real" one?

With a relatively easy-to-make fixture, a mill of some sort, and a single-tooth fly cutter in teh form of a gear toothspace, you should be able to get there. I'd recommend gashing, i.e. removing most of the material with a slitting saw or similar item to reduce wear on your one tooth cutter. You want it to last the whole gear to avoid re-setting too much.

roberlt
08-13-2005, 11:43 PM
J Tiers,
I have thought about using the mill, however IF this method can be made to work it might be interesting to use.

Rob

G.A. Ewen
08-14-2005, 12:23 AM
<font face="Verdana, Arial" size="2">Originally posted by J Tiers:
How about you do it again, and use that "gear" as an indexer to make a "real" one?

With a relatively easy-to-make fixture, a mill of some sort, and a single-tooth fly cutter in teh form of a gear toothspace, you should be able to get there. I'd recommend gashing, i.e. removing most of the material with a slitting saw or similar item to reduce wear on your one tooth cutter. You want it to last the whole gear to avoid re-setting too much.</font>

Good advice. http://bbs.homeshopmachinist.net//wink.gif

winchman
08-14-2005, 01:30 AM
I made the simple gears on this toy

http://img.photobucket.com/albums/1003/winchman/Gear%20Train%20Toy/Gear_Train_3.jpg

by drilling a series of evenly spaced holes at the appropriate diameter in the blank. I used my mini-mill and rotary table.

I used an endmill the same size as the drill bit to remove the material between the holes and the OD. That was followed by a slightly larger endmill to relieve the tops of the teeth for clearance.

The result is teeth that mesh pretty closely and run with a soft whirring sound. The material is frosted Plexiglass.

This simple procedure would probably work for you since the aluminum gears wouldn't need to last forever, and they could be replaced with new ones BEFORE they wore to the point of failure.

Roger

Ian B
08-14-2005, 06:39 AM
Rob,

Exactly what failed? The bond of epoxy to aluminium, or epoxy to brass strip?

If the former, try turning a series of fine square edged rings into the aluminium disk.

If the latter, try scouring the inner face of the brass strip with coarse abrasive paper before feeding it through the rollers.

Obviously, it all needs properly degreasing before bonding. Try letting the epoxy set at a higher tempertaure - the optimum temperature is different for each epoxy, the manufacturer's data sheets should detail this.

Ian

SGW
08-14-2005, 07:36 AM
You might try Brownells's Acra-Weld expoxy, mixed with atomized aluminum or steel for filler. www.brownells.com (http://www.brownells.com)

Could be you're simply asking more of an epoxy gear than it is capable of delivering.

Paul Alciatore
08-14-2005, 12:17 PM
I heard of this technique a long time ago but it was a little different. It was described as a way of making an emergency replacement for a broken change gear while the proper one was being ordered.

Instead of epoxy, they used a low melting temperature, pot metal to cast the gear. A piece of drill rod or shaft was used as a core to form the bore. Can't remember if they also formed a keyway or broached it afterwards.

I have used epoxy to repair broken gears with a variation of this where only a few teeth needed to be replaced. I went to pains to help bond the epoxy to the broken gear. I drilled a couple of holes into the gear and inserted steel studs (cut off wire brads with their surface indented with pliers) into them with epoxy as a preliminary step. They helped to hold the epoxy in place. The repaired gear worked for several months before failing. It took me that long to convince management to buy a new one.

Epoxy may be OK but I would not recommend metal gears of this sort to be used for any long time as they will cause excessive wear patterns on the original gears. It would be better to cut some aluminum or brass gears with a proper cutter.

Paul A.

Peter S
08-14-2005, 06:42 PM
Rob,

What a neat idea for a gear! Even if it doesn't work!

Would it be possible to turn an undercut groove into the OD, ie circumference, of the blank? Like a circular dovetail. It would give the epoxy something to key into.

As has been asked, it depends whether the teeth are breaking up or whether the joint between aluminium and epoxy is giving way.

roberlt
08-14-2005, 07:01 PM
After looking over the remains it appears that the epoxy was bonded to both the aluminum "hub" and the outer tooth form. It looks like the epoxy failed inside the tooth, the brass without support then bent and now teeth are missing. I thank IF I can find a stronger epoxy this idea might work. Does anyone have ideas on a strong (in shear strength) epoxy?

Thanks

Rob

[This message has been edited by roberlt (edited 08-14-2005).]

lynnl
08-15-2005, 10:25 AM
Instead of epoxy, how about melting some pot metal and filling the voids with that?

Another thought I had: that low temperature fixturing metal ...forgotten what it's called. I've never worked with it or even personally seen it, so it may be too soft for that application. Just an idea.

Of course using hot metal to fill it will require some means other than soft solder to join the ends of the tooth-embossed strip.

[This message has been edited by lynnl (edited 08-15-2005).]

ahidley
08-15-2005, 02:18 PM
Why not go to http://www.mcmaster.com/ and buy one for 10-20$?

Evan
08-15-2005, 02:31 PM
Rob,

You may find this thread helpful.

http://bbs.homeshopmachinist.net//Forum1/HTML/006727.html

roberlt
08-15-2005, 09:09 PM
Thanks for the responses.
I din't know if the low melting point alloys would bond to aluminum. I think not but I will look.

If McMaster had the gear I wanted I would have bought it yesterday.. They don't so here I am.

That previous thread is interesting however I have a model A (with QC gearbox)so I don't have extra gears.

Thanks again

Rob

JCHannum
08-15-2005, 09:15 PM
I have no words of wisdom, I do remember the article. I seem to recall Terry used a wood blank and Bondo for a filler.

I just wonder how tight did you set your gears. It will produce a serviceable, but possibly clunky gear, and you might not want to set it up as tight as you would the steel gears. In this application, quite a bit of backlash is tolerable.

roberlt
08-15-2005, 09:38 PM
I have the article in front of me.

Terry says "The earliest ones had timber or plywood centers but later I graduated to brass and aluminum. I never had one fail in service and can recommend the system to anyone lacking gear cutting facilities"

I don't see any mention of Bondo, he says he filled the teeth with "epoxy putty"

When I installed the gear I found the tightest spot (at the solder joint) and set it up with appx. .010 clearance.

Body shops use "Metal to Metal" Bondo I wonder if it might be worth a try?

Thanks for the ideas,

Rob

MechHead
08-16-2005, 09:07 AM
What are the specs for your gear?

roberlt
08-16-2005, 10:59 AM
Gear specs. for the gear (that is failing) are 18DP, 127 teeth, 14.5 pressure angle,3/8 wide, 5/8 inside bore.

If I need to I will cut one, or buy one. However IF this method can be made to work it could be a neat trick to have up your sleeve..

Thanks,

Rob

Paul Alciatore
08-16-2005, 11:28 AM
The 18 DP gears for SBs are hard to find on the new market. You just about have to make or have them made.

However, there are a lot of them sold on E-Bay. Set up a search and be a little patient. You should have what you need in a month or so.

Paul A.

John Stevenson
08-16-2005, 01:39 PM
Rob, Check your email.

Sir John.

gothdog
08-16-2005, 03:58 PM
Here is a technique for increasing the strength of epoxy that I have read about but not tried personally.

Firstly, some polymer resins (polyester resin in particular) can be strengthened by changing the mix ratio of resin to hardener. This is common practice in marine fiberglass repair work but does not work for epoxy.

Some projects I have read about call for epoxy to be strengthened by mixing metallic powder with the resin (I have read variously of aluminum powder or machine filings being used.) You might try this technique and see if it actually helps.

Regards,

--- GothDog --



------------------
In the Elder days of art, builders wrought with greatest care, each minute and unseen part, for the Gods see everywhere -- Longfellow

BillH
08-16-2005, 04:08 PM
<font face="Verdana, Arial" size="2">Originally posted by gothdog:
Here is a technique for increasing the strength of epoxy that I have read about but not tried personally.

Firstly, some polymer resins (polyester resin in particular) can be strengthened by changing the mix ratio of resin to hardener. This is common practice in marine fiberglass repair work but does not work for epoxy.

Some projects I have read about call for epoxy to be strengthened by mixing metallic powder with the resin (I have read variously of aluminum powder or machine filings being used.) You might try this technique and see if it actually helps.

Regards,

--- GothDog --

</font>


That is what JB weld is, isn't it?