Fitting a bushing

[Doggggboy]

I am trying to repair a car lift and need to replace a worn bushing on one of the cable pulleys.
The axle is 20 mm and the pulley bore is 22.5 mm.
Of course I can't find anything that size so my plan is to use a 5/8 x1 inch bushing.
I should be able to bore out the pulley to accept the bushing on the mill, press it in and then bore out the bushing to accept the axle.
This is not a high speed assembly, just routes the cable from the ram to the post at each corner of the lift.
What size should I shoot for to accept the bushing for a nice press fit?
I haven't actually measured the od of the bushing yet, just looking for some guidance on tolerances.
This will be my first attempt at making a useful part with the boring head so I got a pack of 4 bushings at PA.

 

[Darren]

0.001" per inch diameter is a good baseline for most press fits

 

[RobinHood]

I got a pack of 4 bushings at PA.

Did you get the oilite bronze bushings or the steel ones?

I have used both in the past.

The oil impregnated ones are very brittle and require very sharp HSS tooling for best results. If you plan on pressing them “cold”, I would make a close fitting (to the ID) press arbor. I tried without one and the bushing just turned into dust.

What did work was heating the part on the BBQ and freezing the bushing. Then no pressing was required and it dropped right in.

The Offshore oilite material is not nearly as good as the old stuff from Boston Gear (and other vendors).

The steel bushings don’t have the problem of shattering.

 

[Doggggboy]

Did you get the oilite bronze bushings or the steel ones?

I have used both in the past.

The oil impregnated ones are very brittle and require very sharp HSS tooling for best results. If you plan on pressing them “cold”, I would make a close fitting (to the ID) press arbor. I tried without one and the bushing just turned into dust.

What did work was heating the part on the BBQ and freezing the bushing. Then no pressing was required and it dropped right in.

The Offshore oilite material is not nearly as good as the old stuff from Boston Gear (and other vendors).

The steel bushings don’t have the problem of shattering.

Sintered bronze according to Princess Auto.

 

[RobinHood]

Ok, sintered bronze (SAE841) is what I referred to as oilite bushing. Oilite is a trademark product for sintered bronze (oil impregnated bronze).

Oilite® Bearings and Bushings - Self-Lubricating Synthetic Performance Non-Tox and Food Contact Certified

Shop the wide range of Oilite® self-lubricating bearings and bushings including Non-Tox and Food Contact Certified plain bearings, thrust bearings, flange bearings, sleeve bearings, thrust washers in the Oilite® material.

oilite.com

If you are careful, it will work out fine for your application.

 

[VicHobbyGuy]

Loctite (Bearing) retaining compound can help if you don't have a very tight press fit.

 

[Mcgyver]

What size should I shoot for to accept the bushing for a nice press fit?

Sintered bronze according to Princess Auto.

I agree .001 per foot rule of thumb for interference fits, however the sintered bronze type are (or should be) engineered to fit a nominal hole. In other words you should be able able to press a 1" nominal one in a 1" reamed hole and end up with the right ID. ID & OD are oversized. If really keen, somewhere there are the formulas on how to make the ID vary such that you can control the shaft clearance.

From PA I'd check the dimensions, but a sintered bearing should be a press fit in a nominal size reamed hole

 

[Doggggboy]

I agree .001 per foot rule of thumb for interference fits, however the sintered bronze type are (or should be) engineered to fit a nominal hole. In other words you be able able to press a 1" nominal one in a 1" reamed hole and end up with the right ID. ID & OD are oversized. If really keen, somewhere there are the formulas on big to make the hole to vary the shaft clearance.

From PA I'd check the dimensions, but a sintered bearing should be a press fit in a nominal size reamed hole

Well, step one worked out ok.
I got the pulley set up in the vice and went to town with the boring head.
Managed to get from 5/8 to .995 without borking anything.
The bushing pressed nicely into the still warm pulley with no excessive force.
Makes me wish I had a better set of drill bits.
Right now I jump from 5/8 to 1inch.
Pretty sure there are a few sizes in between that would have made this easier.
I'll get after the hole for the shaft tomorrow.

 

[Doggggboy]

Step two was ..okayish?
While milling the excess stickout off the side of the bushing, it broke off but only above the edge of the pulley so that turned out ok.
Boring the center out from 5/8 to 20 mm went alright until the final few passes and then I started to get a lot of chatter.
I was taking .002 off and going about 1000rpm on the slowest auto downfeed on the mill.
I still ended up with a usable bushing but it sounded pretty bad.
Too fast, too slow, too much?

 

[DPittman]

Step two was ..okayish?
While milling the excess stickout off the side of the bushing, it broke off but only above the edge of the pulley so that turned out ok.
Boring the center out from 5/8 to 20 mm went alright until the final few passes and then I started to get a lot of chatter.
I was taking .002 off and going about 1000rpm on the slowest auto downfeed on the mill.
I still ended up with a usable bushing but it sounded pretty bad.
Too fast, too slow, too much?

My guess is that you should slow rpm down to about half that however with only .002" removed that may not be the case. Not alot of help I am...move on, sorry. I will be looking for response as well.

 

[RobinHood]

Those bushings from PA are hard to deal with (see my post above). That offshore stuff is “nasty”.

I think your speed was too fast. IIRC, I had problems boring them out as well. Ended up using very low RPM, like maybe 250, and sharpened (honed) my little cemented carbide boring bar to get a good, non-chatter, finish. Oh, I also used cutting oil even though the material has oil impregnated into it.

 

[PeterT]

I have limited bronze experience but I have had no issues single point turning/boring. Basically I use the same inserts as for aluminum. No problem with fine DOC, finish & accuracy. But tool geometry is very important. Bronze can act somewhat like brass with conventional drills & even end mill cutting angles. Probably the high copper % but anyways can be grabby & then other issues ensue. I only pre-drill with 'dubbed' drills & then single point bore to finish diameter unless the hole is small. Even reaming has a slightly different feel to me vs other alloys. I puta bit of friction on the tailstock feed & I do use a cutting fluid.

 

[Former Member]

One word......CARBIDE.

I would say that since I am doing way more production, I have gone to carbide (99% of the time). Once you figure out the speed and feed changes required, while initial cost is more expensive, tooling last way longer, gives a better finish, flexes less and is sharper.

As to bronze and brass I recall reading (or seeing) somewhere that a 0 or negative cutting edge greatly reduces the grab and pull out experienced in certain materials.

 

[PeterT]

As to bronze and brass I recall reading (or seeing) somewhere that a 0 or negative cutting edge greatly reduces the grab and pull out experienced in certain materials.

That's what I was referring to in post#12. Drills which have been dubbed (exactly as you say, reduced rake) are much better way to go. Regular rake can cause real problems including grabbing & jamming. But the inserts I use are for aluminum (if anything increased rake, polished uncoated, very sharp & tiny nose radius). They turn bronze like a dream single point mode which seems contradictory. So I'm wondering if its a 'degree of edge cutting' thing. A big drill has lots of cutting edge contact vs a turning or boring tool has the typical point. A case of 'it works but why'.

 

[Tom O]

The PA ones aren’t pure bronze a magnet will stick to it.

 

[Susquatch]

Sorry can't help it......

One word......HSS.

I would say that since I am doing way more custom and one-off hobby work/repairs, I have gone to HSS (99% of the time for anything important) and Carbide when convenience matters and results don't. Once you figure out the speed and feed changes are required to use Carbide, you have wasted 15 prototypes and your life is over. That says nothing about initial cost of all the broken inserts getting it right. And then there is the cash outlay for carbide. HSS costs less, lasts way longer, gives a better finish, flexes less, is sharper, and is more easily sharpened.

That was all mostly just said cuz it was fun to use the same words to favour a different horse. But it has a serious side to it too. I prolly cut more stock with carbide than HSS. But I'm old and I'll be dead before I master Carbide to the extent that others do. I don't do production anything. My machining is all one-offs with no opportunity to tune performance. I like carbide for the convenience of just grabbing another one as needed for hogging off metal . But I'm no purist of any kind. In any given application, I use what I have, what I know how to use, and what works for me, and go from there. They each have their place in my world. For now I favour HSS when I get one shot on a difficult task. But I can certainly appreciate other points of view with different experiences and different applications.

 

[Former Member]

I think its just a matter of adjusting to the new cutters, once you get there its second nature like the HSS all of us have originally learned on.

Adaptation is the key.

 

[Doggggboy]

So it looks like I'm going to have to try again with the bushing. The first one fits well enough but I think the original might have been steel.
There wasn't really anything left of the original and it's hard to tell in the remaining hubs for sure without pressing them out. It looks like the other bushings all have a split in them and they seem pretty hard if I go after the edges with a carbide scriber.
Looking at McMaster Carr it shows that the sintered or oilite bushings wouldn't have the strength needed in this application anyway.
They are on the cable pulleys on the corners of a 8000 lb lift. The decks weigh close to 1000lbs and with the vehicle onboard, you're looking at potentially 2250 per corner if evenly balanced.
Mcmaster show a max load of 1500 lbs for this size of bushing.
The lift supplier hasn't been particularly helpful so far.

 

[WilliamR]

I guess you wanted to make your own, but these bearing bushings are pretty cheap. $9 on amazon ca for two 20mmx23mm. Not your size but I'm sure something is out there you could make work. Could probably add some lube slots or? if you thought you needed them. I would post link but not enough posts yet. Lots of similar styles on amazon, flanged and straight.

uxcell Sleeve Bearing 20mm Bore 23mm OD 20mm Length Plain Bearings Wrapped Oilless Bushings 2pcs​

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[Doggggboy]

I guess you wanted to make your own, but these bearing bushings are pretty cheap. $9 on amazon ca for two 20mmx23mm. Not your size but I'm sure something is out there you could make work. Could probably add some lube slots or? if you thought you needed them. I would post link but not enough posts yet. Lots of similar styles on amazon, flanged and straight.

uxcell Sleeve Bearing 20mm Bore 23mm OD 20mm Length Plain Bearings Wrapped Oilless Bushings 2pcs​

View attachment 26484​

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Thanks!
It never even occurred to me to check Amazon,