I've got a couple of little Dana 12 volt air compressors used
to inflate tires. Photos are at
http://nemesis.zefox.com/~bob/dana_compressors/
One of them has broken a plastic pulley and
a few questions come to mind:
First, does anybody recognize and/or know anything about them?
Probably no, but it can't hurt to ask.
Second, the broken pulley was a press fit on a 3/8" shaft with a
shallow spline rolled into it.
Is there any chance an aluminum
pulley with dual setscrews might hold without an impossible-to-
remove press fit using only the setscrews?
https://www.amazon.com/dp/B07RGQJ751?ref=ppx_yo2ov_dt_b_product_details&th=1
Thanks for reading, and any insights!
bob prohaska
Is there any chance an aluminum
pulley with dual setscrews might hold without an impossible-to-
remove press fit using only the setscrews?
"Bob La Londe" wrote in message news:ujauoe$3dh0g$1@dont-email.me...
On 11/18/2023 10:47 AM, bob prohaska wrote:
Is there any chance an aluminum
pulley with dual setscrews might hold without an impossible-to-
remove press fit using only the setscrews?
I'd probably measure the OD of the splines, and if possible see how much runout there is. Then I'd probably do the following to give me the best chance of success.
1. Bore the new pulley to a light press fit on the spline.
2. Mill a keyway on the shaft and broach a keyway in the pulley.
3,. Drill and tap for two grub screws in the pulley. On to bear on the key, and one to bear on the shaft.
4. Drill a slight divot in the shaft for grub screw number 2 so it
doesn't raise a burr.
If I can spin the shaft sans belt and pulley I might try to put a
partial radius on the outsides of the splines for a better engagement as
step zero. I might try it under an end mill.
Bob La Londe
-------------------------------------
That's what I would do too, since I have a milling machine, keyway
broaches, arbor press and a lathe to make custom guide bushings for the broaches.
A lower tech substitute that works fairly well is to drill and tap a
small axial hole where a keyway would go, 1/2 in the shaft and 1/2 in
the pulley, and tighten a short screw into it, secured with Loctite. A
drill bit won't run straight in steel|aluminum but you could turn and
bore a dummy steel bushing to drill and tap the shaft side of the hole straight, then replace the bushing with the aluminum pulley and do its
side. I might drill the hole in both first, then tap them.
An even lower tech fix is to align and tighten the pulley, remove it and
file flats where the setscrews marked the shaft. A second short setscrew
will help lock the first in place.
And then there's Loctite.
At Segway a valuable prototype was mistakenly assembled with the
permanent version of it. Guess whose bench that landed on to somehow
repair.
And then there's Loctite.
On reflection the maximum torque doesn't seem huge.
At 100 PSI there's roughly 100 pounds force on the
piston with a half-inch lever arm. With a 3/16
inch shaft radius it's only 270 inch pounds. Have
I got that right?
The new pulley seems to be coming direct from China
and should arrive sometime late in the month. When
I get a good look at it there will probably be more
questions.
----------------------
The exposed end is the offset crank throw. Push too hard and you might bend it. Pushing against the counterweight may be safer, if you can.
bob prohaska <bp@www.zefox.net> wrote:
On reflection the maximum torque doesn't seem huge.
At 100 PSI there's roughly 100 pounds force on the
piston with a half-inch lever arm. With a 3/16
inch shaft radius it's only 270 inch pounds. Have
I got that right?
Intuition suggests there should be a reasonably
direct relation between press fit force and torque
holding ability, at least when all dimensions are
close to 1. Is there a rule of thumb or table?
A few hundred pounds of press fit wouldn't be very
hard to apply.
Here's a photo (sorry for the blur)
of the compressor shaft: http://nemesis.zefox.com/~bob/dana_compressors/IMG_0031.JPG
Here's a view of the back of the crank: http://nemesis.zefox.com/~bob/dana_compressors/crankcase/IMG_0010.JPG Supporting the crank in a press (vise) or against an anvil might
make it fairly easy to assemble by force.
The tip shaft diameter is .350 inch, the splines
appear to be knurled in before hardening (the shaft feels file-
hard) with a diameter of .355 inch. The basic diameter of the
crankshaft is .375 inch. Looks like I'll have to do some boring.
The pulley bore is .316 or .317, nominally 8 mm.
The new pulley seems to be coming direct from China
and should arrive sometime late in the month. When
I get a good look at it there will probably be more
questions.
The pulley showed up direct from China, postage paid,
in about two weeks. Really rather amazing for $8.65 .
Thanks for reading,
bob prohaska
Jim Wilkins <muratlanne@gmail.com> wrote:
----------------------
The exposed end is the offset crank throw. Push too hard and you might bend >> it. Pushing against the counterweight may be safer, if you can.
understood. Ideally the pressure would be applied in balance on both.
That would require some sort of stepped (or undercut) mandrel.
After thinking it over, I believe the force required to create
a press fit between a smooth shaft and a smooth hole would be
roughly equal to the torque applied at the hole radius needed
to make it slip.
On paper, if the torque generated by the piston/rod/crank was
270 inch pounds a press fit nominally tighter than 270 linear
pounds would be expected to hold. I'm assuming shearing friction
is equal in both axial and azimuthal direction. That obviously
won't be true in my case, thanks to the axial splines knurled
into the shaft.
If somebody sees an error in this reasoning please point it out.
It's not clear I want to use a press fit (disassembly will be
extremely difficult if it's ever needed) but it looks like an
option.
Thanks for reading,
bob prohaska
---------------------------------------- https://amesweb.info/press-fit/interference-fit-calculator.aspx
The sample could be bored in short steps to see how the force increases with the amount of interference. Less than 0.001" can make quite a difference.
You don't have to measure the bore, just keep the last setting. This is probably hopeless on a drill press with the ~0.010" gap between letter sized drills.
No lathe? Then you are limited to buying what you can't make.
There's very little space to bring a puller to bear. At least the
setscrew approach will make further repairs a little easier.
On Sun, 3 Dec 2023 03:15:18 -0000 (UTC)Useful-looking tool. Too burly for my foreseeable needs, but maybe someday.
bob prohaska <bp@www.zefox.net> wrote:
<snip>
There's very little space to bring a puller to bear. At least the
setscrew approach will make further repairs a little easier.
Doesn't matter now... but check out Bearing Separators, may be handy to
know about them someday if you don't already. Short video, ~2 minutes:
https://www.youtube.com/watch?v=JRiMIorP-oQ
Nice repair project you've done there?
The more I think about it the more mysterious the assembly sequence
becomes. Physically it's identical to a large model airplane engine. The cylinder and crankcase are one piece, it looks impossible to dismantle non-destructively. The photos are still at http://nemesis.zefox.com/~bob/dana_compressors/ if anybody's game to
hazard a guess.
On 12/3/23 17:16, bob prohaska wrote:
The more I think about it the more mysterious the assembly sequence
becomes. Physically it's identical to a large model airplane engine. The
cylinder and crankcase are one piece, it looks impossible to dismantle
non-destructively. The photos are still at
http://nemesis.zefox.com/~bob/dana_compressors/ if anybody's game to
hazard a guess.
Remove the cylinder liner.
https://www.youtube.com/watch?v=TuzEco3EDUM
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