[How do I?] Calculate Bore Id To Get An Exact Bushing Id After Press Fit

mattthemuppet2

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Hi all,

I need to put 2 new bushings in the spindle pulley of my Atlas 618. Problem is the bore of the olite bushings I have is 20.10mm and I'm shooting for an ID of 20.00-20.02mm, as the spindle where the bushings will run is 19.99mm chuck end and 19.97mm at the gears end. I bored the temporary pulley to 20.02mm which was a nice sliding fit with a smidgeon of play (by tilting the pulley, no radial play I could feel), which gives me a good number to shoot for on the bushings.

OD of the bushing is 24.00mm and the OD of the pulley where the pushing will be pressed in is ~35mm. Current ID of the pulley is 35.36mm give or take.

The previous bushings aren't any help as one was a very light press fit (if that, I think it spun a bit) and the other was glued in, which may have been the cause for the off-centricity of the pulley.

Anyway. Q is - what do I need to bore the ID of the pulley to in order to squeeze the bushing ID down from 20.10mm to 20.00-20.02mm? I can try shrink fitting (have access to dry ice) or press fitting on my press, although I don't want to risk cracking the pulley. I'd rather avoid any post operations if possible, as I've heard that olite is hard to cut cleanly and still retain it's bearing ability. Plus it'd be another opportunity to screw up the concentricity of the bore and pulley face.

thanks!
 
I think rather than forcing the bushings into the pulley I would investigate swaging them with a steel die.


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Hi all,

I need to put 2 new bushings in the spindle pulley of my Atlas 618. Problem is the bore of the olite bushings I have is 20.10mm and I'm shooting for an ID of 20.00-20.02mm, as the spindle where the bushings will run is 19.99mm chuck end and 19.97mm at the gears end. I bored the temporary pulley to 20.02mm which was a nice sliding fit with a smidgeon of play (by tilting the pulley, no radial play I could feel), which gives me a good number to shoot for on the bushings.

OD of the bushing is 24.00mm and the OD of the pulley where the pushing will be pressed in is ~35mm. Current ID of the pulley is 35.36mm give or take.

The previous bushings aren't any help as one was a very light press fit (if that, I think it spun a bit) and the other was glued in, which may have been the cause for the off-centricity of the pulley.

Anyway. Q is - what do I need to bore the ID of the pulley to in order to squeeze the bushing ID down from 20.10mm to 20.00-20.02mm? I can try shrink fitting (have access to dry ice) or press fitting on my press, although I don't want to risk cracking the pulley. I'd rather avoid any post operations if possible, as I've heard that olite is hard to cut cleanly and still retain it's bearing ability. Plus it'd be another opportunity to screw up the concentricity of the bore and pulley face.

thanks!
20 mm equals .7874". More than likely your Atlas lathe originally had imperial nominal sized bushings and shafts, not metric. I am guessing someone along the line may have already changed them from the original sizing. If it was me I would buy 3/4" ID by 1" OD bushings and turn and bore them to the ideal sizes that I wanted, ID and OD. The ID will get smaller when you press in the bushings. Amount smaller depends on the press fit. I would aim for about .001 to .002" press fit and expect the bore to get smaller by most of the press fit amount. I have turned Oilite bushings, ID and OD, and they are quite easy to resize. You just need to make sure you are using a sharp, positive rake grind on HSS tools. If not, you run the risk of smearing the sintered bronze and plugging the oil pores. You will still probably need to finish the ID's to final size after installing the bushings, and that is a good thing.
 
I think rather than forcing the bushings into the pulley I would investigate swaging them with a steel die.

thanks for the idea, but that's quite a long way beyond my ability and I'm not sure it'd do the olite much good

20 mm equals .7874". More than likely your Atlas lathe originally had imperial nominal sized bushings and shafts, not metric. I am guessing someone along the line may have already changed them from the original sizing. If it was me I would buy 3/4" ID by 1" OD bushings and turn and bore them to the ideal sizes that I wanted, ID and OD. The ID will get smaller when you press in the bushings. Amount smaller depends on the press fit. I would aim for about .001 to .002" press fit and expect the bore to get smaller by most of the press fit amount. I have turned Oilite bushings, ID and OD, and they are quite easy to resize. You just need to make sure you are using a sharp, positive rake grind on HSS tools. If not, you run the risk of smearing the sintered bronze and plugging the oil pores. You will still probably need to finish the ID's to final size after installing the bushings, and that is a good thing.

oh for sure Bob, they're almost definitely imperial measurements, but the metric olite bushings are what I have to work with. thanks for the tips about boring them, I do have a boring bar long enough (I think) to bore both to size at the same time, so that's definitely an option if necessary.

so, I've done the math (!!) and found that to reduce the bushing ID to 20mm I need to reduce the bushing OD (and therefore ID of the pulley) to 23.916mm, which in old money equates to a 0.0033in press fit with the current 24mm OD of the bushing.

Is 0.0033in doable into an alu/zamac pulley? Will I get that in by heating the pulley (to ?C) and freezing the bushing, or will it need pressing in?
 
Hi all,

I need to put 2 new bushings in the spindle pulley of my Atlas 618. Problem is the bore of the olite bushings I have is 20.10mm and I'm shooting for an ID of 20.00-20.02mm, as the spindle where the bushings will run is 19.99mm chuck end and 19.97mm at the gears end. I bored the temporary pulley to 20.02mm which was a nice sliding fit with a smidgeon of play (by tilting the pulley, no radial play I could feel), which gives me a good number to shoot for on the bushings.

OD of the bushing is 24.00mm and the OD of the pulley where the pushing will be pressed in is ~35mm. Current ID of the pulley is 35.36mm give or take.

The previous bushings aren't any help as one was a very light press fit (if that, I think it spun a bit) and the other was glued in, which may have been the cause for the off-centricity of the pulley.

Anyway. Q is - what do I need to bore the ID of the pulley to in order to squeeze the bushing ID down from 20.10mm to 20.00-20.02mm? I can try shrink fitting (have access to dry ice) or press fitting on my press, although I don't want to risk cracking the pulley. I'd rather avoid any post operations if possible, as I've heard that olite is hard to cut cleanly and still retain it's bearing ability. Plus it'd be another opportunity to screw up the concentricity of the bore and pulley face.

thanks!

Oilube (an Oilite competitor) used to provide the formulas for pressing their bushings into bores so as to not disturb the sintered running surface. You might Google them (I think they're still in business) to see if this info. is available. As stated above, machining or reaming could seal over the oil delivering pores of the bushings.

Edit: I Googled "Oilube". It's a product name & not the company name. They post the sizing info in the full catalog on pages 4 & 5. Page 5 gives the bore size data. Of course it would wise to compare Oilite specs to Oilube to be sure.
 
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Is 0.0033in doable into an alu/zamac pulley? Will I get that in by heating the pulley (to ?C) and freezing the bushing, or will it need pressing in?

Read the technical information on the manufacturer's site. I seem to remember that heating the bushings too hot can clog up the pores with carbon soot from burning the oil in them. Also, there are a lot of different types of "oilite" bushings, with different amounts of porosity, different lubes (some Teflon), and other differences, some minor, some major. Make sure you understand the process and the issues. If the bushings are an unknown type you had on the shelf, I would be tempted to just buy a couple that exactly fit my needs and are a known quantity for checking the manufacturer's recommendations. They are not that expensive...
 
I haven't used much Oilite, maybe its easily compressible but I wouldn't think so. As a general rule .001 - .0005 per inch of dia is a pretty snug press fit. The .0033 your shooting for would take a lot of force to push in cold , a shrink fit with that much interference would probably result in the same split pulley.

Greg
 
I haven't used much Oilite, maybe its easily compressible but I wouldn't think so. As a general rule .001 - .0005 per inch of dia is a pretty snug press fit. The .0033 your shooting for would take a lot of force to push in cold , a shrink fit with that much interference would probably result in the same split pulley.

Greg

+1 on what you said.

Tom S.
 
Maybe turn the bushing to size, knurl the od and bore the id close to finished dia, maybe .010 over. Smear the knurl with JB Weld and press in. After the JB hardens, I think it's somewhere near 17 hours, bore the id to size.​
 
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