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GT1
01-11-2014, 09:37 AM
I am making a new output shaft for a gear box. The original tapered roller bearings were pressed on. Based on the dimensions I have taken, there appears to be about a 0.001" interference fit. The bearing seats are located in each half of the housing and the preload on the bearings is based on a spacer (and a gear) between the bearings. By maintaining the same stackup height, I can maintain the same preload as the original setup. Would there be a problem in using a light press fit (0.0002-.0003) and the Loctite bearing mount instead of the press fit for the bearings. I have always disliked heavy press fits for fear of damaging the bearings.

jlevie
01-11-2014, 11:27 AM
If the design is right and the bearing is pressed in correctly, there should be little chance of damaging the bearing. I'm going to guess that the housing will contain gear lube and it may degrade Locktite over time. I'd stick with the press fit.

lakeside53
01-11-2014, 12:08 PM
I agree.

Heat or cooling can help the fit. Pressing in the correct place will not harm the bearing.

Doozer
01-11-2014, 01:10 PM
The ID race of the bearing will just hoop larger
when pressed over the shaft. One thou is no
problem.

--Doozer

MrSleepy
01-11-2014, 02:27 PM
If your serious about doing it properly..

First you need to find out the type of tolerances (of the bore ,shaft,housing and the bearing) for the forces and loads your bearing will be subject to.


Nobody can definatively tell you .... "just use 2 or 3 thou under or over" ..... because based on the loadings and forces your bearing may need to have the casting heated for a tight fit to hold the bearing under load ....or maybe not .... maybe a looser fitting will suffice.

Industrial Maintenance Manual (http://www.timken.co.uk/EN-US/products/Documents/Industrial-Bearing-Maintenance-Manual.pdf) .... http://www.timken.co.uk/EN-US/PRODUC.../Catalogs.aspx (http://www.timken.co.uk/EN-US/PRODUCTS/Pages/Catalogs.aspx)


The Timken website has lots of information , and the Industrial Maintenance Manual (http://www.timken.co.uk/EN-US/products/Documents/Industrial-Bearing-Maintenance-Manual.pdf) at the bottom of the page gives you selection charts based on the shaft , housing bore and bearing type, and bearing tolerances (E8 to S7 (E8 (loose) to S7 (very Tight)).

Page 33 onward gives you advice on a 12 point procedure for selction of the correct data and from pg39 onward it goes into the tolerence selection charts.

You maybe able to obtain some idea of the loads and tolerances based on the original bearings chosen by the OEM.

Rob

lakeside53
01-11-2014, 04:22 PM
..and... surface finish has a lot to do with "fit". If you don't have a TP grinder, polish to final measurements with emery.

GT1
01-11-2014, 07:50 PM
Gentlemen, thanks for the replies. I had not thought of the effects of the oil on the loctite, so based on that reason alone I will go back with the press fit. The maintenance manual provided some interesting points, specifically regarding a ground finish on the shaft. The original shaft appears to be ground. The new one will be fabricated on the lathe, so polishing with emery will have to suffice. The bearing area on the original shaft is very good condition and I can get accurate and repeatable dimensions. Getting ID measurements with telescoping gages on the ID of the bearing is far more difficult. The measurements are in general agreement with the published numbers but I can't reliably measure to the 0.0001 on the ID. So I have to assume the published nominal measurement for the bearing ID. Since I have a reasonably accurate number for the OD of the shaft, I will shoot for that. I will use HSS to make all of the final cuts to provide the best surface finish and minimize the polishing to preserve the "roundness" of the shaft. The 0.001" interference fit I calculated based on the as found conditions is midway between a medium and heavy press fit and seems appropriate given the operating conditions. I have already made driving sleeves for the inner races. So with the appropriate chamfers, surface finish, dimensions, assembly lube and perhaps a little heat, maybe this project will be completed next week (still waiting for a woodruff cutter to complete the shaft).

rklopp
01-11-2014, 11:27 PM
Rather than a press fit, it's a lot more fun to heat the bearing in hot clean oil and then drop it onto the shaft. It's less likely than pressing to cause damage, too. If you change the interference from the original design, be prepared to change the axial spacing arrangement that sets the preload, due to the change in radial clearance. If you take the shrink fit route, do your math so you know how hot to heat the bearing and give yourself plenty of margin.

GT1
02-06-2014, 02:13 PM
Just a follow-up, mission accomplished. I retained all of the original dimensions for the shaft along with generous chamfers. I polished the bearing seats with emery cloth and some Mothers until they were shiny. A little bit of anti-sieze and the bearings were pressed on to the shaft with no drama. Initially, I tried freezing the shaft and heating the bearings, but due to the high humidity in the shop, ice crystals immediately began forming on the shaft when removed from the freezer. Fearing long term corrosion by trapping water along the shaft, I decide against this. The smooth finish seemed to be key. When the bearings were pressed on, they progressed very smoothly.

daGrouch
02-06-2014, 02:35 PM
Gotta love it when a plan comes together! :D