Thin workholding suggestions

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Glenn Brooks
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Thin workholding suggestions

Post by Glenn Brooks »

Looking for suggestions how to hold down down some 1/4” plate to make 3/16” or maybe 1/8” thick fingers for my Van Norman Dividng Head.

These ‘fingers’ are missing on one of the two DH I purchased. I would like to replace them so when I pass it on to someone else it is a complete and functional unit.

So now contemplating the workholding is something of a night mare. I am figuring most of the work will be down on my mill and rotary table.

BTW, there are two separate parts here. They stack on each other and slide around the shaft. Hold in place with a small, fine threaded screw.

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2D32D697-7484-404D-BA4F-470CEE293EA9.jpeg
0ED49807-8A1F-4875-98F6-42E1CD8E1628.jpeg

Any suggestions would be greatly appreciated.

Thanks
Glenn
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whateg0
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Re: Thin workholding suggestions

Post by whateg0 »

I would do as much as I can before thinning down the fingers. Clamp the part to the rotab and machine the inside round features. Then clamp the part to the rotab and machine the outside profile. Last, machine the fingers to thickness. I've never used the superglue method, but depending on how you are able to get ahold of it, or not, that might be a good solution for at least the last part.

Dave
SteveM
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Re: Thin workholding suggestions

Post by SteveM »

How dare someone sell you one like that :-)

Don't discount finding one on ebay. I've seen them for sale there.

You just need to match the hole size (or if it's larger, make a spacer).


Steve
Glenn Brooks
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Re: Thin workholding suggestions

Post by Glenn Brooks »

Yes, who ever heard of a DH with missing parts! Imagine that... And where did all the chucks wander off to? In the case of Chuck Van Norman, he who wanders is lost indeed! I checked the thread pattern on the spindle also, thinking to find an old used cushman, union or similar chuck. Ahahahahahaha. Couldn’t even find a google reference to a 1.875 x 16 TPI spindle size.

I disassembled the finger assembly today and cleaned it up on the wire wheel bench grinder. Thickness of each part is .093”. So just under .100”. Actually, with paint, when new, right at .100”. The fingers are half of that, but triangle shaped, probably for strength. Also the parts are mirror Images of each other. Which brings up the idea of gluing two plates together and milling one shape out of the stack, then separate the two half’s and finish the fingers separately??

Anybody use Loctitie cylindrical bonding compound as a glue down technique? I think it is has greater shearing strength than super glue.

Thanks
Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
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tornitore45
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Re: Thin workholding suggestions

Post by tornitore45 »

Start with a piece larger than you need. Clamp it down flat on areas outside of the part footprint. Reduce the thickness without machining your clamps. Machine the inclined surface before contouring. When contouring leave thin webs every so often to keep the part from braking off. Cut the webs at the end, by hand with a saw or a chisel.
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ctwo
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Re: Thin workholding suggestions

Post by ctwo »

You can clamp the piece in a vise with a piece of stock on one side. Side mill the exposed side of the part with it trapped between the mill and fixed jaw. You can angle the vise to get a tapered finger. You can make it longer to cut off waste stock, or with a stop move the stock to the other side and finish machine the thickness.
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Harold_V
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Re: Thin workholding suggestions

Post by Harold_V »

One thing to keep in mind is that flat material has a tendency to bow when you remove stock from either side. If you hope to keep the parts flat, it's a good idea to remove material in steps, alternating shallow cuts and flipping the part, so a roughly equal amount of stock is removed from both sides.

To achieve the best possible results, rough the entire part before taking any finish cuts. That way all the surfaces will blend properly.

This is a good instance where you'd be best served to start with hot rolled material instead of cold rolled, which has a lot more internal stress than hot rolled. Both will work, however, it's just that cold rolled will be a little more challenging.

H
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Bill Shields
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Re: Thin workholding suggestions

Post by Bill Shields »

as much as I like and use the Loctite products, this is not really a place for them.

If you were surface grinding to size....MAYBE, but milling ->

I would use one of the suggestions from above...and as HV says - stay away from CRS...you want something stable.

You might find ground to size HRS to be a reasonable choice -> I use it for many things.
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Glenn Brooks
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Re: Thin workholding suggestions

Post by Glenn Brooks »

Bill, where would I look for a short piece of ground to size HRS? Are their any on line vendors? We have little to no speciality metals places around Seattle anymore...

Thanks,
Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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NP317
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Re: Thin workholding suggestions

Post by NP317 »

Glenn:
Onlinemetals.com
They are physically located at the SE corner of the Ballard Bridge in Seattle!
Walk-ins are welcome. You can cruise through several shelves of scrap ends, or get the catalog materials.
Check them out online to see if they have what you want.

I've used them for 20+ years, including my time at the Univ. of Washington, and still do. The business was started by two cousins who lived on Queen Anne Hill. Near neighbors to us.
Then they sold to Krupp Industries, and their offerings accelerated. Multiple US locations now. Not cheap, but good.
~RN
whateg0
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Re: Thin workholding suggestions

Post by whateg0 »

I wish onlinemetals.com was closer. Their prices are generally ok, but they get on the shipping, it seems.

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Re: Thin workholding suggestions

Post by tetramachine »

Those look like steel, mostly I see brass bronze in the Quadrant bar (fingers). If me I would take a piece of steel, brass about 5/16 thick, layout the parts and trace them on blued. Then cut the profile ,150 doc, when finished flip the stock , machine off the excess on the back side. The only thing left to do would be that angle to the edge.

There is a X power feed on the mill, so you set the long side in that axis. Set the feed slow, and use Y to cut outside the layout lines, grind to final shape later. When doing the round portion, feed x-y separately , sort of bump cutting, feed in a bit of y, then x to the line, back off x then feed more y, then x and back off. The effect will look like a gear that stripped its teeth, Then take it to the grinder,(belt works best for these) and quickly it will be round.
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