Author Topic: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor  (Read 569 times)

Offline vtsteam

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What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« on: April 10, 2022, 10:23:29 PM »
Here's a little item I laid out 45 bucks for  :wack: :wack: :wack::

MSC Expanding Machinable Lathe Arbor, 2-1/2" Face Diameter x 4" Length

What's wrong with this picture?

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline PekkaNF

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #1 on: April 11, 2022, 01:46:46 AM »
Here's a little item I laid out 45 bucks for  :wack: :wack: :wack::

MSC Expanding Machinable Lathe Arbor, 2-1/2" Face Diameter x 4" Length

What's wrong with this picture?

Dunno, could be many things. One problem might be thin wall on stub, that expanding screw looks relatively thick.

Offline Sea.dog

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #2 on: April 11, 2022, 03:54:38 AM »
A tiny screwed taper trying to move large chunks of steel. The centre hole and taper should be much larger.

Offline RussellT

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #3 on: April 11, 2022, 05:46:21 AM »
I'm not sure that the screw looks long enough to engage the unslotted part of the arbor.

Russell
Common sense is unfortunately not as common as its name suggests.

Offline vtsteam

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #4 on: April 11, 2022, 08:52:39 AM »
Seadog has it. Everything else in the ad description is truthful. It WAS 2-1/2" in diameter. It WAS a mandrel. It DOES fit in a lathe, and it IS machinable.

It just doesn't expand. 

Well, I take that back. If you take the 8mm Allen wrench supplied and cut with a grinder to a straight length and then weld that into 1/4" pipe, then make a 4" Tee handle for it, and try to expand it with that wrench and find it still doesn't expand perceptibly, so you slip a 8" pipe cheater over the new wrench handle and apply force until the expansion screw stops in a tight jam almost impossible to undo even though you greased everything with high pressure grease, you will get a measured .005" of expansion. Only at the very tip of the far end.

Who in their right mind thought that a small screw would perceptibly deflect six 3" long pieces of 1" thick tool steel enough to grip a part in a lathe? A part, which, to slip onto the 4" long arbor, needs at least .005 inches of clearance in the first place?  And the available .005" expansion only achievable with an oversized dumb-donkey wrench and cheater bar?

How can MSC ship these things out with a straight face? Have they ever tried one? Was it an April Fool's Day special, and I didn't notice?

Ya know it's not unusual for me to buy "cheap" tooling (this wasn't cheap btw) since it's what I can afford, and then have to correct something, or find a way to live with some small issue, or for it to have limited life, or a rough finish, etc. But this is a first..... where the simple purpose of a tool is so completely and obviously missing. An expansion arbor that doesn't expand. What were they thinking? That no one would notice?

I mean it seems obvious in hindsight, and embarrassing, not comprehending for several hours, so sure that it must work, that I went to the trouble of making a bigger wrench for it, somehow still believing that those 1" thick jaws would move. Of course they can't! Just look at the damn thing, Steve!  :hammer:

And ya know, I had a bad feeling buying it in the first place. It was a stretch, 45 bucks for something fairly simple, that I have made myself in the past (much smaller, however). But I thought, Steve, just buy it, that will let you get on with this engine build, without taking on yet another tooling project. Grow up, you don't have to make everything. The engine is the important thing. Get this thing and be done with it.

And the cool thing was, it was machinable, so it would fit the 2.400" bore I needed to hold. So naturally I did machine it before finding it wouldn't grip the part. I got a nice tight sliding fit. Both loose, and unfortunately with the mandrel "expanded"! So the return option wasn't available.

Anyway, what to do......

Well, notice the following ad, also found on Ebay. See any difference? And these are smaller -- 1-1/2" 1-3/4" and 2"...

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline RussellT

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #5 on: April 11, 2022, 01:31:31 PM »
Anyway, what to do......

Well, notice the following ad, also found on Ebay. See any difference? And these are smaller -- 1-1/2" 1-3/4" and 2"...

I think you're going to have to try machining that groove!
Common sense is unfortunately not as common as its name suggests.

Offline vtsteam

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #6 on: April 11, 2022, 01:49:29 PM »
Right Russel!

So, how deep should we relieve this thing? Well, looks like the properly made set has a 1-1/2" diameter version, and it was found necessary there to add relief -- so checking that photo and enlarging it, it appears to me that the relief cut is a little shallower than the chucking stub. And checking their specs in the advert, that stub is 1" dia. So the relief cut must be less than 1-1/2" dia and more than 1" dia in depth.

I make that out to be 1-1/4".  :smart:

Okay out with the parting tool.......
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline djc

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #7 on: April 11, 2022, 02:38:26 PM »
I think your expectation of 0.005" expansion is a little ambitious. This is approximately the same figure used as an OK measurement for 5C collets. Compare and contrast a 5C collet to what you have and perhaps reconsider.

Offline vtsteam

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #8 on: April 11, 2022, 05:28:10 PM »
This ain't a 5C collet. I've made these before.

Also what 5C collet would work with inch thick walls? And an R8 closes down ten times what a 5C does. Chalk and cheese.

Here, good explanations and types of shop built expansion arbors illustrated. Note the relief cut on even a small diameter aluminum version, and the grip range.


I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #9 on: April 11, 2022, 08:57:46 PM »
Turning a relief slot. I went in a half inch -- the example arbors would have meant going in 5/8", but already I have 10 thou expansion now with reasonable hand tightening of the wrench instead of 5 thou wrestling a cheater pipe extension on the wrench to get it.

Ten thou is a reasonable tightening range, since a typical tube part requires about 5 thou clearance to slip onto the arbor before tightening. Another 5 thou of range gives a good enough grip for what I need

The original supplied 8mm Allen wrench gave no expansion at all prior to modifications and before the bigger handle wrench was made.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #10 on: April 11, 2022, 09:05:14 PM »
Facing a flange on a thin wall stainless steel displacer cylinder for a Ryder engine driven by the corrected expansion arbor and held in the new steady rest.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Sea.dog

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #11 on: April 12, 2022, 03:17:33 AM »
I still see a problem with the setup, Steve. The tiny taper is, as you have realised, only expanding the end, so it's hardly presently a parallel clamping force in the bore of your workpiece. The taper needs to be much, much longer and more gradual.

Offline vtsteam

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #12 on: April 12, 2022, 09:17:09 AM »
Well technically yes, but practically, that's how this type works, and I indicated the outside of the tube true in the 4 jaw after expansion.

It's main purpose is as a driver, like a lathe dog. as long as the tubing itself is centered at that end and at the steady rest end, the small taper grip isn't a problem. Unless it slips -- which was the problem before.

Because the arbor is initially turned to a fairly close fit on your part, it has much less tendency to distort the tube walls than chucking a tube directly, even with a spider. And the 6 jaws instead of 3 or 4 is also helpful in that regard. Not perfect but certainly usable. There are more advanced expansion arbor designs for higher precision than is needed here.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline ddmckee54

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Re: What's Wrong with this Picture??? MSC 2-1/2" Expanding Arbor
« Reply #13 on: April 12, 2022, 01:46:19 PM »
And here I thought that "Horrible Fright" was the only place that sold tool "kits". 

At least you got it to work for you, so you're not exactly out 45 bucks.  You're just out the time fixing it, that you'll never get back.  I suppose you could try billing MSC, but I wouldn't hold my breath waiting for a response.

Nice save.
Don
Too many irons, not enough fire.