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Thread: Tolerence for press fit bushings
03-08-2011, 06:38 AM #1
Tolerence for press fit bushings
I am new to machining. I recently got my milling machine all set up and running. Now I have many projects planned. Right now I am in need of the proper tolerance to press fit bronze bushings into 14 gauge square tubing. I was told -.005 would be the best fit. I need to buy a chucking reamer and want to make sure I get the right fit.
.5610" reamer would be -.0035" to -.0045"
.5625" reamer would be -.002" to .003"
.5640" reamer would be -.0005" to 0015"
Am I correct on these?
Here is what I am working with;
Bronze Type: SAE 841 Bronze
Type: Sleeve Bearings
Certificate of Conformity: Without Certificate
For Shaft Diameter (Inside Diameter): 3/8"
Inside Diameter Tolerance: +.0005" to +.0015"
Outside Diameter: 9/16"
Outside Diameter Tolerance: +.0020" to +.0030"
Length Tolerance: ±.005"
Load (P Max): 2,000
Speed (V Max): 1,200
Load at Speed (PV Max): 50,000
Any and all help would be greatly apperciated.
03-08-2011, 07:05 AM #2
What ever "tightness" you select is up to you. You possibly realize the important part is the bushing bore after it is pressed in. Tighter fits just mean this will be smaller.
You have said nothing at all about what must fit in the bushing bore, or what size it might be.
There have been special non cutting sizing tools made for sizing 841 bushings since machining the material just closes up the pores that let the oil out of the bushing.
03-08-2011, 07:18 AM #3
I will be using a 3/8 x 2-1/4" shoulder bolt through the bushings. The specs. for those are as follows.
Material Type: Steel
Steel Type: Plain Steel
Head Style: Socket
Head Diameter: 9/16"
Inch Thread Size: 5/16"-18
Shoulder Diameter: 3/8"
Shoulder Diameter Tolerance: -.002" to -.004"
Shoulder Length: 2-1/4"
Shoulder Length Tolerance: ±.005"
Thread Length: 1/2"
Thread Fit: Class 3A
Rockwell Hardness: Minimum C32
Thank you for your help so far.
03-08-2011, 07:39 AM #4
If it were my job:
I would have steel bushings welded in the square tube and ream them for .0005/.0010 press fit for the 841 bushings.
Then I would SIZE (not ream) the 841 to fit the shoulder bolt as needed. These bolts are, after all, very loose tolerance on the OD and the bush may need no sizing at all.
03-08-2011, 08:04 AM #5
03-08-2011, 09:06 AM #6
Unless you specifically need the bronze for temperature range look into Igus bushings, they will live far far longer and need no resizing, just ream the hole to fit. The idea of welding a bushing into the tube aint a bad one.
No way in hell do you need -5 thou of press fit. 1-2 thou under is going to make installation darn hard. -5 thou and your going to have difficulty getting them in. If its a oil lite material then most the oil will get squeezed out and you will have to size the bore (how ever you decide to do it)
Some times you just need to take a good stab at things and try a few sizes to get the fits you need. Boring a few holes out might be a quick way of doing that, once you know the size that achives what you need then get a reamer!
03-08-2011, 09:23 AM #7
not enough zero's?
Methinks you misplaced a zero to the left of the decimal point
I.E. I think you want an interference of .0005
My rule of thumb is .001 per inch of dia
This will give you a snug fit
PS: there's always loctite 660 if you really screwup
Don't ask me how I know this!
03-08-2011, 09:26 AM #8a ball sizer
You shove it through the bore
You don't "get" them, you make them for the job at hand.
03-08-2011, 09:34 AM #9
03-08-2011, 10:10 AM #10
03-08-2011, 11:09 AM #11Your funnin us again
03-08-2011, 11:34 AM #12
Interesting tool, first time I ever saw one.
03-08-2011, 12:04 PM #13
I'd go with around .001 press fit. Also, as has been mentioned a larger diameter requires a bit more press fit. I'd also apply some loctitie to the bushing. It helps assembly as a lube and then helps keep it in place.
Also, whatever you have for a press fit, you need to take off of the ID. That is if it is a precission fit.
Also, I did do some parts were I made a round ball on the end of a shaft. It was a hard material and I polished it. Then I pressed it through a hole to get the hole to an exact size. I can't remeber if the part had some air metering aspect to it or not. I think I reamed, then reamed to very near size before this.
03-08-2011, 12:32 PM #14
TOO MUCH press fit is one of the worst things that gets done quite often, it just ends up shaving metal off an other bad things, some folks think "if some is good, more is better".
When the hole gets accidentally bored so the bushing slips in, then gets cleaned up well with lacquer thinner, roughed a bit with some 80 grit, then glued in with red loctite the end result is a lot better than when somebody decided .003" was the proper press fit for a drill bushing liner :-).
03-08-2011, 01:00 PM #15
The rule of thumb as far as I know was .001 per inch of OD bore.
If you press a 5.005 bushing into a 5.000 bore you best bore the bushings ID to 5.006"+
Never make a bushing too tight, it will shear off the press fit and just fall out later..
03-08-2011, 06:59 PM #16
The old Boston Gear catalogs (the "pocket-sized model" from where John might have extracted that sizing tool sketch) contained much useful information about installing and running oilite bearings as well as other helpful information about shafting and gearing.
I'm not sure that the new catalogs include the same stuff. (If not, too bad since the pocket-size edition morphed into a collection that now takes up over six inches of room on my bookshelf and I hardly ever look at them !)
03-08-2011, 07:09 PM #17
Machinery's Handbook has several pages of info on press fits and running clearances. As a newbie to machining, you might want to pick up a copy - it's been in print for many years and the old editions are just as good as a new one.
03-08-2011, 07:20 PM #18
I think johnoder's idea about welding in a steel bushing first is essential.
If you put a bronze or plastic (Igus) bush into a transverse hole in a tube, it will be supported only by the tube wall. Most of the length of the bushing being unsupported will deflect away from the load and the resulting actual bearing area will be very small. It will wear out/pound out very quickly.
03-08-2011, 08:20 PM #19
The press fit on a .500 OD valve guide for a 350 Chevy is .002”. Perhaps this is to allow for heat expansion. On an iron liner for repairing an engine block it is .0005” per inch of bore. So a sleeve to press in a 4.000” hole you would have .002” press fit. In both cases it is typical to hone the ID after installation for final sizing.
Just some press fit tidbits from my world.
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