View Full Version : Bronze Bushing Clearance?

10-22-2007, 12:17 AM
When working at small dia's the necessary rpm has my gear train just screaming. They howl so bad my family shuts the door to hear the TV. I realize they're straight cut gears and ain't never gonna be dead quiet, but I went poking around in there anyway.

As a typical example, my tumbler gear bushings are out to .628-.629 and the shafts they ride on are .622 or so. Cheap and easy would be standard replacement .625 bushings but I wouldn't be adverse to making my own custom fit bushings to what's left of the shafts.

Is this a worthwhile idea? If so, what clearance should I use?

Thanx again


10-22-2007, 12:51 AM

What you have is a fairly large clearance.What about needle roller bearings and races?They can be had from Torrington with intregal seals for not much money.

10-22-2007, 02:34 AM
Use PTFE bushings and make them zero clearance. They will work fine at those loads and rpms. Plain virgin PTFE is good to a PV factor of 1000. The PV factor is the Pressure in psi times the Velocity in sfpm. That means a PTFE bearing will withstand 1000 psi at 1 sfpm or 1000 sfpm at 1 psi or any combination in between that doesn't exceed the value 1000. That value includes a 100 percent safety factor. The PV factor goes up two to three times if oil lubricant is used.

10-22-2007, 03:40 AM
I made a number of bushings for my Rockwell from plain old Enco cored Bearing Bronze. Several shafts had moderately intricate features that I didn't really want to duplicate, so I just turned them a bit under, just enough to clean them up, and made new bushings to match. Easy enough and worked quite well I think.

oil mac
10-22-2007, 07:06 PM
My Myford Super 7 Has as standard tumbler reverse gears made of Tuffnol( which was standard) When she is running on high spindle speeds pretty she is pretty silent
Might be an idea for you to consider, for peace on domestic front

10-22-2007, 08:53 PM
All good ideas. and will all work.Some times so grease will help to.

10-22-2007, 09:06 PM
I've wondered if there would be much difference in the noise between the stock steel gears in most gear trains versus swapping out for a couple of brass gears? What do you guys think?

Rich Carlstedt
10-22-2007, 09:25 PM
Yes...alternated brass/steel/brass will do it to.

10-22-2007, 09:31 PM
Yes...alternated brass/steel/brass will do it to.

Rich, would it make a big enough difference in sound to make it worth replacing a few gears in the geartrain with brass ones. I wouldn't mind trying if it would make a noticeable diffenence but hate to do it and then hardly even be able to tell they are in there. What do you think?

10-22-2007, 10:29 PM
You can also use "open gear grease" to quiet noisy external gears. It's a thicker, gummier grease (more or less depending on brand) that cushions and stabilizes the gear meshing. I started off using the ISO 68 on my Rockwell to avoid the (significant) mess. But then ordered some Enco spray stuff that did quiet things noticeably, though not dramatically.

10-23-2007, 10:00 AM
I put a plastic 20T? gear on the reversing tumbler of my Craftsman lathe and the noise reduction was several orders of magnitude. I think the plastic gear will probably last quite a while, especially if the junk is kept out of it.

10-23-2007, 02:39 PM
If you really want to quiet the gears down use the black tar like open gear grease on them. It will take more than 75% of the noise out and they will last longer. However, if you get the grease on you or anything else it is hard to get off. You can also use it on the bushings. It lasts a long long time and a little of it goes a long way.