OK all you MEs and PEs and all you knowledgeable folks.
I’m looking to interference press fit into cast truck side frames 3x6x3 (mm) ball bearings. How much of a press fit can I get away with without killing the bearing?
About .0001" or less. Might even want to make it net.When I pressed steel axles into my cast iron wheels for my 1.5" trucks, I was told to give it .001. These are .750" diameter.Broke the wheel right away! From then on, I used .0002"-.0003". 30 years plus later, they never moved!
Tolerances like that give me the willies.
Make it size for size, then taper the start of the bore just a smidgen to start the bearing. And always press on the outer race of the bearing!
Dave,
What are the materials involved? So long as the material of the journal is softer than the bearing material, you only need be careful to not crack the journal. Size on size with a wipe of Loctite will work fine.
Bob c
@Bob It’s a hard Pewter alloy ( w/ copper and silver). I was hoping for size on size, but I was concerned on “loctite” as the potential of locktiteing the bearing.
The bearings are the Metric equilivent of a 1/4" across with a 1/8" hole and 1/8" thick. Perty tiny things, and they dont look like they would take much force to mess them up.
Would slight clearance, say .0015 and locktite in be a better fix sense the stress load from GR really won’t be an issue?
@Dave - I don’t see why, for the hobby stuff we do, that a -0/+.001 tolerance wouldn’t work. What I was trying to get across with the Loctite was a dab on the end of the finger and just a touch to the outside race of the bearing. Just enough to hold it in place.
Bob C.
I have a hint, which I will preface with a comment: I hate Super Glue/ACC, etc.
But in lieu of locktite, #222 may not be strong enough in this application. I have used super glue in combination of metal to plastic and metal to metal, so long as the ACC doesn’t get wet it is very strong. Trying to extract a SS 4-40 or 6-32 in a hole with ACC the head will come off before the screw body releases.
Barry
Barry,
The reason I recommended the Loctite was that it will flex a little with the temperature differentials of the metal bearing and the (most likely) plastic truck side frame. There are also several different ‘flavors’ of Loctite as well, some you can only make release with a torch (not quite what we are looking for). I have used the Loctite 242 with great success in many applications.
Bob C.
Pics?
Well OK, this wasn’t intended to be a build log, but I’ll show ye all what I’m trying to do… I’ll try to shoot a couple of pics.
Bottom line is that I will have to build new side frame masters with larger journal boxes to fit the ball bearings into… My first try on the new journal boxes i’ll chock up to experience.
Bob C.
I use 222 mostly since I need loctite on small bolt threads and set screws. But I have 242 and few others, 242 has worked well for me.
The use of AC was a surprise to me, and then discovered it was still working after a long time period (a year or more). Also thought it was good information to pass on.
Thanks, Bob.
Barry
1st UP… I’m NOT trying to go into truck making and selling business… These will be for me first and a few friend.
I had been casting my side frames from a “Cerro blend” low temp metal. The “Cerro” metal has proved to be less then what I wanted, for the frames. Wanting to move to a stronger metal, My research led me to a Hard Pewter blend, hardened with copper and silver. This blend needs to be poured at 600+ degrees, and I’m having to heat the molds to 300 deg. To handle this temp, i’ve had to make new Molds from High Temp RTV that will handle these much higher (more then 400 degrees higher) temps.
Heres what I’v been able to come up with.
(http://i1234.photobucket.com/albums/ff403/dave2-8-0/TRUCKS/Trucks04_zps30907f66.jpg)
(http://i1234.photobucket.com/albums/ff403/dave2-8-0/TRUCKS/Trucks03_zpsdab17aba.jpg)
I’m wanting to mount ball bearings, and hence where i’m at now. The bearings are to large to mount into this trucks journals. (iPhone pics, not so good up close).
(http://i1234.photobucket.com/albums/ff403/dave2-8-0/TRUCKS/Trucks05_zps6a7de476.jpg)
Im starting to carve up the new journals for a new set of side trucks.
(http://i1234.photobucket.com/albums/ff403/dave2-8-0/TRUCKS/Trucks02_zps4cf2225c.jpg)
If anyone see anything i’m doing wrong, Don’t hesitate to let me know.
Silly thought, since you appear to be planning on tossing these molds anyways… Couldn’t you just take an exacto knife to the journal cavity and widen it a tiny smidge? You wouldn’t have to go all the way, just on the back half a bit more than the thickness of the bearing race.
That would save you the work of new masters & new molds if you could pull it off.
In either case, your originals look great. They’d make great additions to anyone’s layout.
JD, Silly me… I hadn’t thought of that!! I wasn’t thinking of tossing these molds. They work great as originally designed, and I’ll still use these Molds for non roller bearings.
I hadn’t thought to just modify the master, maybe with a thin piece of plastic, just enough to give some meat to the journal to hold the bearing, and make a new mold as a prototype…
As there were never intended to be prototypical show trucks, but every day runners, a little cheating would be just fine by me.
I’ll keep you posted.