press fit lube?

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liveaboard
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press fit lube?

Post by liveaboard » Fri Nov 15, 2019 3:42 am

I'm going to press a 25mm mild steel shaft into a hole; it's a crankshaft for my reciprocating hedgecutter and there will be torque.
So the fit is tight.
I need maximum friction after assembly, but I'm a little concerned about damage during pressing, or the parts getting stuck halfway.

Should I use some sort of lubrication?
I don't have access to any propitiatory lubricants [except wd40].
I have bearing, lithium, copper, and silicone grease, got motor oil, way oil, cutting oil, graphite. gear oil, brake fluid, soap, wax, elbow grease, etc.

I'm almost done making the parts so I'll probably be pressing it together by tomorrow.

Harold_V
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Re: press fit lube?

Post by Harold_V » Fri Nov 15, 2019 4:01 am

How large is the item in which you'll press the shaft? Wall thickness will play a large role in how much press will be beneficial, or tolerable. Also, what is the nature of the materials you're using? Mild steel on mild steel has a tendency to seize. If that happens, you'll end up with an assembly that most likely won't run true, and you may or may not be successful in a full insertion, even with a lot of tonnage.

Have you given any thought to heat shrinking the assembly? That's a real good way to put things together. If you think it would work for you, might help to describe the pieces in better detail. If it will work, I'd think a thou and a half interference (.04 mm) would do an admirable job, assuming the hole has sufficient wall thickness. Assuming the piece with the hole will tolerate the required heat, you can heat the piece with a barbecue, or even a torch. Get it hot enough and the two pieces will slip together without issue. Once cooled, you'll not get them apart. It wouldn't hurt to cool the shaft, too. Dry ice will work, but lowering its temperature in a freezer will help some.

H
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liveaboard
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Re: press fit lube?

Post by liveaboard » Fri Nov 15, 2019 5:18 am

I used an online interference fit calculator; that came up with about the same number as you recommend for dimensions.
The hubs are highly eccentric, and also mild steel. It's really difficult for me to obtain anything else [it's a problem I will be working on in future though].

The hubs are 85mm diameter and 20mm thick, and the offset is 19mm from center.
I usually do heat fit this sort of thing, but in this case I need time during assembly to get the radial lineup correct. I need to partially fit the parts, then mount it in the lathe and center them to each other, then continue pressing.

My first one failed; it has 500 hours on it and it's toast.

This one is a bit heavier and I'm using Self Aligning Ball Bearings on the crank pins that can tolerate a lot of misalignment [the pushrod position can be off too]. The ends will be finished after assembly so they'll be parallel for standard bearings.

So a bit of error is ok but I'm trying to get as close to correct as I can.

So; try and fit dry?
If it fails, I'll survive.

I can drill into the edge of the hub afterwards, tap and add a lock bolt through the pin. I did that with the first crank I made; but I sort of like the idea of a press fit that does the job.

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Bill Shields
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Re: press fit lube?

Post by Bill Shields » Fri Nov 15, 2019 7:40 am

white lead
Too many things going on to bother listing them.

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liveaboard
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Re: press fit lube?

Post by liveaboard » Fri Nov 15, 2019 8:39 am

I don't have any white lead, and can't seem to source that in Europe.
Maybe banned here; lead phobia, don't know.

Russ Hanscom
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Re: press fit lube?

Post by Russ Hanscom » Fri Nov 15, 2019 10:24 am

Not going to find white lead anywhere unless you have a 50 year old container stashed somewhere.

We have been using never-seize for the RR wheel pressing, seems to work fine. Surface finish is also a big factor. Burnishing the surfaces reduces galling.

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NP317
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Re: press fit lube?

Post by NP317 » Fri Nov 15, 2019 10:41 am

I have used LocTite adhesives as lubricants during pressing.
Then they set up and the assembly is secured.
No galling was experienced with mild steels.
RussN

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liveaboard
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Re: press fit lube?

Post by liveaboard » Fri Nov 15, 2019 1:14 pm

I was thinking of using loctite; I have a tube so that makes it a good choice for me.

I realized I need the paint some areas I won't be able to access after assembly; so it will be a few days before I press it together.
crankshaft parts.jpg

Mr Ron
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Re: press fit lube?

Post by Mr Ron » Fri Nov 15, 2019 4:01 pm

How about a tight fit and a weld bead to lock
Mr.Ron from South Mississippi

Harold_V
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Re: press fit lube?

Post by Harold_V » Fri Nov 15, 2019 5:10 pm

Given the conditions you described, I think my choice would then be to use any of the anti-seize compounds readily available on the market. I would not try a dry press unless one of the components was heat treated. Good idea that the parts not have any "dirt" on them when you do the assembly.

H
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Re: press fit lube?

Post by liveaboard » Sat Nov 16, 2019 7:30 am

There is very little available here in rural Portugal; I have copper grease anti-seize compound.

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Re: press fit lube?

Post by Harold_V » Sat Nov 16, 2019 5:00 pm

I suspect that, by now, you've made the assembly. How'd it go?

H
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