INTERFERENCE FIT SPLINES

[SKinzel]

We have some splined couplings that are designed to have an intference fit of .002-.004 on the teeth. The spline is 23T 8/16 DP 30°Pa spline.

I'm trying to figure out how hot the coupling hub needs to be to assemble onto the shaft. I know how to do this for regular circular bores but I'm not sure about the spline teeth/spaces. Does anybody think that if I treated like a regular bore with the same OD and calculated the temperature for growth needed that would cover me?

My first thought was to calculate measurement between pins for a larger space width and heat the couplings until we hit that measurement but I don't think that is practical since things are going to be pretty hot and the pins will heat up before a good measurement can be taken. Not to mention the danger of working that closely with hot parts.

These couplings are going on a straightener gearbox with 17 shafts and of course this has to be done ASAP so I don't have time for trial and error.

 

[dinjin]

If you do not have the time to experiment, who does?
Expansion is expansio. Can you freeze the shafts?
Contraction is contraction. Who designed this without
specifying how they are to be assembled?

 

[gearcutter]

Does the spline specification call for a side fit or a major diameter fit?

.002"-.004" seems like a lot for this relatively small pitch.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[SKinzel]

One of our other engineers along with one of our business managers (guys who do routings and costing for the jobs) decided on the fit.

When I was asked I thought, after parts were manufactured and ready to be assembled, .004 sounded pretty tight for the pitch. We currently do not have access to the ANSI spline standard which I hope would have some guidance on tight fit splines.

When the shop was heating the coupling they put on an bearing induction heater and weren't able to get the coupling on. I don't remember what temperature setting they used. To compound matters, the leading edge was not chamfered like it was suppose to have been and the parts may have missed the deburr stage as well. When things get in a rush like they were for this job people skip the "small" but very important steps.

Right now I'm mostly concerned with trying to figure out how much heat we have to put into the coupling hub to get the space width to grow enough to allow assembly. I've never had to do that for splines and since the space width is small compared to the overall mass of the coupling and taking pin measurements isn't practicle.

 

[carburized]

Splines usually have a side fit, major dia fit, root fillet fit etc. No matter what you have, if it is a interference fit, you could freeze the shaft. Use Liquid Nitogen to freeze the shaft. This way you will not ruin the geometry of the shaft. But be careful, not to overfreeze the shaft.
We do this in our one of the geared products.

http://www.gearsandbearings.com

 

[SKinzel]

I haven't heard back but the spline is a side fit. The shafts are assembled in a gear reducer (17 shafts total) so freezing is a little difficult. When I find out how things went I'll update.

Now I'm really curious as to some guidelines on how to calculate thermal growth in a coupling bore that is splined. I'm wondering how close it would be to use the pitch diameter and see what temperature difference is needed to grow that diameter the necessary amount. The curvature of the space width flanks is what makes me not sure how to calculate the temperature needed.

With some luck my boss will okay the purchase of the ANSI spline standard which may contain some info on tight fits.