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tmc_31
10-17-2009, 06:08 PM
Hi all,

I am building a manual collet closer for my lathe. The tube is 1.5" O.D. nominal DOM. It mic's out to be 1.502" O.D. . My handle is mystery aluminum. I want to bore the hub for a press fit. What should the I.D. of the hub bore be? I have a 10 ton hydraulic shop press that I would like to put this together with.

Thanks,

Tim

SGW
10-17-2009, 06:36 PM
My method of doing a "press fit" has always been a close sliding fit and Loctite 609. But, if you really want to press it, I'd probably try about 0.001" interference for that diameter.

Peter.
10-17-2009, 06:36 PM
For something like that I'd make the hole .002" under the OD of the tube and heat the alloy handle before fitting.

clutch
10-17-2009, 07:28 PM
I tend to use 0.001" per inch of diameter. If it really matters, I get out Machinerys Handbook and read it.

Clutch

tmc_31
10-17-2009, 07:41 PM
Thanks guys,

I think I will try .001 under.

Clutch I looked in Machinery's HB, but being a newbie, I was not sure where to look. I searched (I have the PDF on my computer) under press fit and found only references to plastic materials. If you have a specific reference in Machinery's that would be helpful, I would enjoy reading it, if you wouldn't mind posting it. I also looked in Wikipedia and the engineers edge website. The engineers edge also referred to .001-.002 clearance but it was for steel on steel. I don't know if it makes any difference.

Oops, should have searched under "interference fit". Found lots of references.

Tim

Rich Carlstedt
10-17-2009, 10:06 PM
.001 to .0015" per inch is a standard formula for interference fits.
So yours at .0015 to .002 is right there.
You are correct about disimilar metals and interference fits.
Particularly when Aluminum is the bigger part, as it expands at 175% of the rate of steel.
On your 1.500 bore, this means if you raised the temperature of the steel tube 100 degrees (F) it would become (.0000063 x 100 x 1.5=) 1.5009
and the Aluminum would become (.000011 x 100 x 1.5=)1.5016 or growth of .0007 greater.

As long as the temperature stays constant, you will have no problem.
As you can see, if you heat the Aluminum 300 degrees more than room temp, the .002 fit disappears, and it is size for size.
I would make the parts .002 different, and mark the aluminum with a magic marker, and then heat it up. When the felt tip mark disappears suddenly (gets very light) you will be about +400 degree over room, and slip it together.
please know this, a shrink fit has twice the break-away torque of a press fit, with the same interference numbers.

Rich

tmc_31
10-17-2009, 11:17 PM
Rich,

Thanks, I am still boring the hub slowly, sneaking up on the final diameter. Looks like I will need a final I.D. of 1.500" on the hub to have a .002" interference (tube is 1.502" O.D.). Will this press together in the hydraulic press without heat? I may want to adjust the handle's position on the tube later, once I get the internal threads on the tube cut.

If it is going to require heating the hub, can I reheat it and move later if I need to without damaging the handle?

I had thought about putting the tube in the freezer for 24 hours, but given the different rates of expansion between the aluminum and the steel, it looks like I will get more bang for my buck by heating the handle. Is this right?

Thanks to all of you for your help,

Tim

MondosMetals
10-18-2009, 12:07 AM
If you plan to use that 10 ton press I would suggest making the mating surfaces as smooth and polished as possible. That alu may not like having a piece of steel jammed down it's throat and could suffer some scoring and galling making dissassembly later on a small challenge. The press will still take it apart, but I wouldn't place any bets on the condition of the aluminum surface once pushed apart.

Freezing the steel may facilitate easy assembly but you won't get it apart that way unless you find a way to freeze the steel while keeping the aluminum warm. If you have designs of taking this apart again later then heating the assembly in an oven at 400F should let it come apart more easily. Handling parts at that temperature present certain safety issues, of course.

:)

tyrone shewlaces
10-18-2009, 04:19 AM
I really, really prefer to apply a shrink-fit when it's possible, even when a press is handy (there are exceptions, like pressing bearings in place which is just too quick & easy for a press, etc.). It just seems to function much better.

As long as the diameters are machined to the right sizes and you heat up the outer part plenty, it's cake. Well, it's cake as long as it slips to where it goes fast enough that it doesn't seize together in the wrong place, which is kind of a bummer.

I can pretty much guarantee that if you press an aluminum slug into a steel sleeve (or vice-versie) that it will shear enough aluminum in the process that you'll only end up with about a .0005 max. actual press fit anyway no matter how much interference you start with.

Dealing with the heat and doing shrink fits are a little intimidating if you haven't done it before, but once you do it you'll have learned sumthin' and then you won't hesitate in the future when it comes up again. It's not tough and man, that thing will be in there and tight.

Pressing it in will work too, but I'm just sayin'...

clutch
10-18-2009, 06:09 AM
Look under ALLOWANCES AND TOLERANCES
Clutch

Carld
10-18-2009, 11:23 AM
Yep, .002" interference fit and heat the handle and quickly slide it in place on the tube. Use a clamp on the tube to stop it where you want it to be because you won't have time to slide it around to where you want it.

DON'T press it on the tube.

tmc_31
10-18-2009, 02:26 PM
Ok guys,

The consensus on in this thread seems to be to bore the handle to .002 under and then heat the handle to 400 deg F., then slide it on.

I just happen to have a propane grill in my shop that should heat the handle nicely.

Thanks fellas, I will give it a go

Tim

Glenn Wegman
10-18-2009, 03:33 PM
200 to 250 above ambient should be good.

I'd turn the shaft on the area to be pressed into the handle just to clean it up and insure it is round. If you leave a very small shoulder you won't need any sort of stop to insure it goes on the desired length. Then bore the handle accordingly.

Just a suggestion:)

tmc_31
10-20-2009, 09:02 PM
Hi all,

I bored the handle so that I had a .002" interference fit. I then heated the handle to 400 deg on the propane grill. I had an old pryrometer from my appliance repair days that measured to 600 deg F. (for calibrating ovens I think). After the handle reached 400 deg I let it set at that temp for about 15 minutes to heat soak. I set the tube in a vice with a stop on it where I wanted the handle to be located. I put the hot handle on the tube and tapped it down lightly. It slid into place very easily. Awesome!! I now have a very nice hand collet closer custom made for my jet lathe.

This was very much a community project. I want to thank this community for all your advice.

Tim