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post #1 of 19 Old 01-05-2018, 05:19 PM Thread Starter
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machining for an interference (press) fit

I need to machine the inside of a 5' schedule 80 aluminum pipe to accept a bearing in each end. I do not have access to a lathe with a chuck that allows for gripping the outside of the pipe. Do the experts here think this would be possible:
Get a step drill bit with its maximum size correct for the bearing and put it in the freezer until cold.
Put the aluminum pipe over a fire to get it warmed to about 300-400 degrees.
Machine pipe bore with bit in drill as quickly as possible. If machining time gets too long (as bit heats up and pipe cools); stop machining, place bit back into freezer and pipe back into fire.
Start again until complete.

I know it sounds silly, but the correct tools are cost prohibitive. My thinking is that if I get the pipe hot (larger) and the cutting tool cold (smaller) while machining then after machining when the pipe returns to ambient temperature (and size) my bearing will *hopefully* press into the pipe with enough interference to hold it in place.

Any thoughts or better ideas would be appreciated.


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post #2 of 19 Old 01-12-2018, 07:07 PM
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Re: machining for an interference (press) fit

How are you going to center your drill? Your description is a bit difficult to understand. Drill bits, in general, drill bigger than the stated size but depends on many factors (like not using cutting fluid). Look for a local machine shop?

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post #3 of 19 Old 01-14-2018, 01:48 PM
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Re: machining for an interference (press) fit

Instead of all that... Why not get a pipe expander...

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post #4 of 19 Old 01-14-2018, 02:20 PM
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Re: machining for an interference (press) fit

Schedule 80 pipe probably will be mighty tough to "expand",unless your using a hydraulic press type machine...even aluminum..

One method I've seen to mount bearings to pipe is to make 2 or 4 bolt flat flanges,weld them to the pipe, and get the pillow block bearing with the 2 or 4 bolt flange mounts and bolt them on..
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post #5 of 19 Old 01-23-2018, 03:41 PM Thread Starter
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Re: machining for an interference (press) fit

Quote:
Originally Posted by nobog View Post
How are you going to center your drill? Your description is a bit difficult to understand. Drill bits, in general, drill bigger than the stated size but depends on many factors (like not using cutting fluid). Look for a local machine shop?

JK
Hmm. I tried to make it as clear as I could. I need to fit bearings in the ends of a 5' long thick-walled pipe. I'm not sure if even a typical machine shop can machine the inside of the pipe, because they would either need some sort of a through chuck or a pretty big lathe with a support. I guess that will be my first stop, but I am also concerned about cost.
edit: I see now that I never mentioned the pipe size. It will be a 5' long piece of NPS1 or NPS 1.25 pipe. Not a 5' diameter pipe! Oops!

Yes, I am afraid the drill bit will drill too big. I need a press-fit from inside of pipe to outside of bearing. That's why I am wondering about cooling the bit and heating the pipe with a torch. Otherwise, I would need to file the outer diameter of the step-bit to make it a smidge smaller.

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Originally Posted by Justy37 View Post
Instead of all that... Why not get a pipe expander... https://www.youtube.com/watch?v=zcz6CSVmxQU
Because that will not work. It would be thick-walled pipe and I need to press-fit the bearing into the end of it, not permanently distort it bigger.

Quote:
Originally Posted by Tractor-Holic View Post
Schedule 80 pipe probably will be mighty tough to "expand",unless your using a hydraulic press type machine...even aluminum..

One method I've seen to mount bearings to pipe is to make 2 or 4 bolt flat flanges,weld them to the pipe, and get the pillow block bearing with the 2 or 4 bolt flange mounts and bolt them on..
The flange idea will not work in my situation. The pipe will end up rolling on the ground after this contraption is finished (think lawn striping kit).


Tom

Last edited by CobraX739; 01-23-2018 at 03:43 PM. Reason: clarity
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post #6 of 19 Old 01-23-2018, 03:58 PM
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Re: machining for an interference (press) fit

Maybe put an "axle" on the end of the pipe and use the flange bearings on a bracket on each end mounted to the deck or tractor ,to allow the pipe to roll freely then ?..

You could weld a thick washer to the pipe that has a large bolt welded to it like a 5/8" or 3/4" to use as an axle..oh wait..your using aluminum...that aint gonna work..

A good machine shop will have lathes with a chuck that will open up to 2" or more ,but its going to cost you to get them to do just 2 pipe bores ,they usually dont want jobs that take longer to set up than to do it ...


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post #7 of 19 Old 01-23-2018, 04:30 PM
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Re: machining for an interference (press) fit

If there was a hole saw that was the correct outer bearing diameter, you could drive a wooden plug in the end of the pipe, carefully mark a center and drill the depth to taste.

Option would be to buy a close fitting pipe internal diameter hole saw and mount it backwards in the outer (bearing diameter) hole saw and use the inner for a centering guide. This will take a bolt to make the drill shank.

Having a lathe, I would turn a loose fit internal pipe size rod and cross drill in a turning point for the bearing I.D. Then add a drill shank and use a hand drill.


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post #8 of 19 Old 01-23-2018, 04:44 PM
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Re: machining for an interference (press) fit

Quote:
Originally Posted by Tractor-Holic View Post
Maybe put an "axle" on the end of the pipe and use the flange bearings on a bracket on each end mounted to the deck or tractor ,to allow the pipe to roll freely then ?..

You could weld a thick washer to the pipe that has a large bolt welded to it like a 5/8" or 3/4" to use as an axle..oh wait..your using aluminum...that aint gonna work..

A good machine shop will have lathes with a chuck that will open up to 2" or more ,but its going to cost you to get them to do just 2 pipe bores ,they usually dont want jobs that take longer to set up than to do it ...
It's not just that the chuck opens up to 2" or more (as all but small lathes do that), but the through-hole needs to be over 1.5" in diameter. I've got a 14-40 lathe, and I think the through-hole is right around that diameter...
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post #9 of 19 Old 01-23-2018, 04:50 PM
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Re: machining for an interference (press) fit

I would look around at machine shops to have this done. There are lathes out there with beds over 5 feet long.
Another idea may be to have a short length of your pipe, machine out the bearing pocket as needed, then weld this onto your long pipe to make your longer pipe...... just thinking out loud....


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post #10 of 19 Old 01-23-2018, 04:54 PM
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Re: machining for an interference (press) fit

Thread the pipe on both ends
Machine a short coupling
Coupling would have female thread on one end
And a shrink fit for the bearing on the other
Use steel pipe
To bad you are not closer
My lathe has an 8 foot bed
5" has to be on steady rest
1.5 can be done thru headstock
I would thread on lathe
Machine threads are more accurate and can be dialed with precision to get the whole mess straight
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post #11 of 19 Old 01-24-2018, 12:39 PM
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Re: machining for an interference (press) fit

Had a thought..
A 3/4" I.D. shaft collar is 1-1/4" O.D.--if one would fit inside your pipe,you could weld a 3/4" bolt to the shaft collar, and then drill holes in the pipe and tap them,drill into the shaft collar part way too--and use short bolts or allen set screws to secure the shaft collar inside the pipe,then you'd have the bolt sticking out to use as an axle..you could double up two shaft collars,if one does not seen wide enough to prevent any wobbling of it inside the pipe,or let the bolt go off kilter..


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post #12 of 19 Old 02-10-2019, 06:27 AM
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Re: machining for an interference (press) fit

How much has to come off for the bearing? Why not just ream it? You can buy a cheap adjustable reamer, they arent great but would work, just need to grind the seam down first. If you have a lot to take off then get a drill bit that's slightly undersized to remove the bulk of material first.

How precise does this need to be?

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post #13 of 19 Old 02-10-2019, 07:44 AM
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Re: machining for an interference (press) fit

A custom axle or drive shaft shop could handle this. Sounds similar to a custom drive shaft which is machined on both end to accept a flange for a u joint or slip joint. Not sure what they would charge but they would also make sure it is straight and balanced if this is a rotating application. Just a thought.
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post #14 of 19 Old 02-10-2019, 09:04 AM
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Re: machining for an interference (press) fit

Quote:
Originally Posted by TooManyGT View Post
How much has to come off for the bearing? Why not just ream it? You can buy a cheap adjustable reamer, they arent great but would work, just need to grind the seam down first. If you have a lot to take off then get a drill bit that's slightly undersized to remove the bulk of material first.

How precise does this need to be?
That would be my thought. reamers are much better at sizing a correct size hole then a drill get it close with a bit, then ream it to size with a adjustable reamer.

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post #15 of 19 Old 02-10-2019, 09:27 AM
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Re: machining for an interference (press) fit

Not sure how much material has to come out of the pipe but you could use a sandpaper flap wheel or a cyl hone. I've used both before to enlarge a hole.
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