What's new
What's new
By:
Advanced search…

Fixing Bearing Bored in Nylatron

Parkerbender

Parkerbender

Stainless
Joined
Dec 19, 2009
Location
Kansas City Mo, USA
So, I have a bunch of bearing bores to cut in nylatron, and the first 30 came out big. 1.372 bore ended up 1.385 after the parts dry! In any case... so what does a person do with those?

Application is 8" diameter pulleys which run 5/16" nylon rope, 1.375" od, 17mm ID roller bearings, both sides. These pulleys will have the correct size (well, or way undersized depending on the temp and humidity) holes on the other side... does a guy dimple them with a spring punch, or wipe some mineral oil on them, or what is the right idea? They get out to 1.385 after a bit of baking, but stabilize around 1.381" in room conditions after dried out.

Now I am just cutting them .010" under where I was, being's you can press fit those bearings in that nylon if it was .015" small if you wanted to, and rather have the holes too small than to big... but I still have 30-some pieces of spendy nylatron gsm 8" round that have some slightly big holes in one side...
 
Dimpling or soaking aren't fixes, I think the best you can do is ask the customer if you can bore and sleeve with a slug with a minimum of ~3/8" wall for stability. Make the interference fit enough, with both parts at the same temp and humidity, so that you'll have good mechanical stability - I'd think around .005".

I'd also take some 6-32 SS flathead screws and drill/tap/ctsk at the interface line to set them flush to mechanically key the parts together. Stake the heads into the part with a sharp punch to ensure they won't back out.

If the customer won't go for it, congrats, you've got some stock for larger hole projects.
 
Bore larger and sleeve, or scrap and start over if the customer can't have a sleeve in there.
Next time, bore them .05" small and let them set overnight to see if they grow.
I've never had problems with Nylatron moving, but UHMW will move on you overnight that's for sure.
 
Why are you drying them? Under normal conditions they will re-absorb the moisture and return to their original size. Better you should soak them in water. If the raw material was stored at room conditions, it will take time, but they will eventually return to that condition.

Alternately, use filled acetyl, delrin. Its stable.

Tom
 
I just read the description again, and am now thinking that if there's a roller bearing being pressed in I'd just ask to make an Al or steel sleeve at a good press into the material, perhaps with a lightly knurled OD to help key it in when the material relaxes after the press. It would actually be more stable than the bearings being pressed right into the plastic itself.

Why the heck are they using that material as a pulley when using roller bearings? I'd have gone for a more stable plastic, or a phenolic composite.
 
I have no idea why they are using that material, the way these guys operate that decision is above my head... Maybe I will punch them out and throw some sleeves in there though it sucks to sleeve 30 of them... Just barely big and if it were me, I would personally just leave them as that if they get a little hot that plastic will just grab the damn bearings anyway and be good again.

In any case, I suppose I will do it right like a good boy... after I let these parts sit outside for a day and see if they shrink back. the ones that I didn't dry out good only got .0015" over. The part that made me dry them out in the first place was because the prototypes ended up like way over (.010-015") so that made me feel like that absorbtion was going to be an issue. Crazy, being's that the damn parts are only in the machine for 3:50 getting that side put on.
 
Have the bearings already been purchased? maybe they can buy a slightly larger OD, then machine the parts to fit...again.
 
Why the hell are you using 1.375" Od bearings with a metric ID? It would be better to run 35mm OD which comes in at 1.378" Might solve your problem. Ball bearings with Inch Od's are specials, AFAIK.
 
I ran into the same problem with some NyloilMDX gray 7" material.I sleeved some and used Tolerance rings on others.It took about a month for them to stabilize.Although some I sleeved also got bigger and the sleeves loosened.Part of the problem was the temp environment the were subjected to.
The oem wheels were blue nyloil and the bores were knurled from the factory,which didn't last.I had better luck with black Delrin.There is a little bit more to these wheels than just a simple flat belt pulley and I thought that the NyloilMDX would be more stable and wear better,but chasing the bores was a big pain.
In your case the load may cause the tolerance rings to wear or extrude the bore because of the load.
My case centering had to be maintained and load was secondary.
 
This is nylatron gsm, I didn't design the parts or spec the material, or buy the material for that matter... everything about what the parts are is overkill, and just decided to heat the parts up good and give them a good whack with the rubber mallet. Shrunk them right back to bearing holding diameter. I didn't spec the bearings either, or anything. That said, there are two 1.375 OD, 17mm ID roller bearings, 1.5" apart on a 8" diameter pulley to run a 400 lb load a total of ~100 ft rope length, a couple times an hour, a couple times a day. Could literally skip the bearings and just run the nylatron on the shafts.

Thanks for the help though, and if there ends up being a concern at all, that locktite was my plan for if giving them a good whack didn't work.
 
You must log in or register to reply here.

Similar threads

J
O/T: a strong bear and 20th anniversary
Replies
19
Views
596
PDW
P
D
Loctite to hold bearing inner race in place?
2
Replies
26
Views
3K
Peter from Holland
Peter from Holland
Crowne
Holding Timing Belt Pulley Stock in 16C collets?
Replies
11
Views
900
Crowne
Crowne
S
Best compromise for less than ideal main bearing bolt design?
2 3 4
Replies
64
Views
4K
tdmidget
T
N
Cat40 spindle rebuild: Thoughts on floating bearings outer races spinning in housing
2 3
Replies
48
Views
3K
Stirling
S








 

ABOUT PRACTICAL MACHINIST

With more than 10.6 million unique visitors over the last year, Practical Machinist is the most visited site for metalworking professionals. Practical Machinist is the easiest way to learn new techniques, get answers quickly and discuss common challenges with your peers. Register for the world’s largest manufacturing technology forum for free today to stay in the know.

Learn more about us.

STAY CONNECTED

Facebook Instagram YouTube LinkedIn Pinterest Twitter Tiktok

Register Become a forum member. Register today.

Sign Up Sign up for our e-newsletter.

© 2024 Copyright Practicalmachinist.com. All Rights reserved.

Back
Top