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Old 06-13-2019, 10:08 PM
o7oBaseMetal o7oBaseMetal is offline
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Default Concave groove radius tool for lathe.

I built a tubing roller a few months back, maybe I will get around to posting photos of that later. The tubing roller will kind of do flat tubing like square or rectangle without dies (though Dies would do a nicer job) but it definitely won't do round tube without dies. I got a pretty good deal on a foot of 3" 8620 steel so I decided to make a few dies to roll round tubing. Only problem, being new to the machining end of the spectrum, I don't have much tooling yet. Basically a small lathe and a drill press. I did a bunch of looking around the internet and decided to make something like this guy made.
https://youtu.be/4pfnGvVN82s

Here is my version, design dictated mostly by materials on hand and the tooling I have on hand.

Also, one finished tubing die. It definitely didn't come out as perfect as I had hoped. There is a bit of slop in the mechanism for spinning the cutter and also more flex than I care for in the lathe. I started out trying to use a small piece of HSS for the cutter but it wouldn't stay sharp. One thing that is tough is there is not much clearance for the chips to break away and they clog up. I ended up replacing the HSS cutter with a 1/4" indexable carbide tool from Harbor Freight that I cut short enough to get the necessary clearance for a 1" groove.
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  #2  
Old 06-13-2019, 11:49 PM
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That die looks pretty danged good for what you have to work with.
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Old 06-14-2019, 09:35 AM
o7oBaseMetal o7oBaseMetal is offline
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Originally Posted by cutter View Post
That die looks pretty danged good for what you have to work with.
Thanks.

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Old 06-14-2019, 11:11 AM
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As Cutter said, it is very good for the application. In general you don't need a perfect round die for bending. One source for dies cheaply is pipe bender dies from chinese benders, often available at yard sales.

There is a thread here somewhere on someone making a die for bending pipe and square stock. For square stock you need to have a rib of 3/16" round rod in the center of the die to concave the inner part of the bend. This will absorb the excess material on the inside of the bend.
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Old 06-14-2019, 11:17 AM
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It might take a couple parts, but you will figure out the sweet spot for the cutting. It looks simple enough.


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Old 06-14-2019, 07:26 PM
o7oBaseMetal o7oBaseMetal is offline
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Kinda tough trying to focus the camera and hold the tape at the same time. I had less 1" tubing around than I thought, originally I was going to do 2 full circles about 3' diameter and put a rolled section of sheet between them for a nicer fire pit than the hole in the yard I have been using for the last 15 years.
So I took the only piece I had and rolled it until it was bent 180°- I actually went a little bit past but it is pretty close. It is approximately 17 5/8" diameter on center so I guess that makes it just shy of a 9" radius. Quite a bit tighter than I intended the roller for but it is nice to know it can roll this tight- I have a feeling I could roll 3/4" Sch. Pipe into sweeps with this same set of dies if the need ever arises but it will be close.
So basically, 1" tubing A36 1/8" wall, not much deviance in the bend area as one direction measured 1.1" o.d. and the other direction measured 0.9" o.d. on the caliper. Even the unbent section had variations by that much so I feel pretty happy about the way it turned out.
Things I would change is that I would put a key way into the drive die (the reason I didn't was simply because I don't know how to cut a keyway in a hole) but I can retrofit a keyed hub from the Farm store easy enough, and also I would like to case harden the dies as they are already starting to show wear. Other than that, I feel like it has been a great learning experience for a guy who has a lot of experience with fitting pipe, welding, and fabrication but very little on the machine tool end of the spectrum.Click image for larger version

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  #7  
Old 06-14-2019, 09:09 PM
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greywynd greywynd is offline
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To cut a keyway in a thru hole, you need to either use a broach, which is pushed thru and cuts as it goes, or a shaper, with a reciprocating tool shaped to cut the keyway.

Broaches are often sold in sets to cover a range of standard sizes, and there is a bushing that goes into the hole, that then guides the broach as it’s pressed thru.


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Old 06-14-2019, 09:39 PM
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Quote:
Originally Posted by greywynd View Post
...To cut a keyway in a thru hole, you need to either use a broach, which is pushed thru and cuts as it goes, or a shaper, with a reciprocating tool shaped to cut the keyway...
If you've got the tools that's definitely the way to go but if you don't use a "Dutch Key". Drill a hole anywhere on the line where a shaft and hub meet and thread it for a setscrew. Makes a pretty sturdy joint...
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Old 06-14-2019, 11:10 PM
o7oBaseMetal o7oBaseMetal is offline
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Quote:
Originally Posted by LKeithR View Post
If you've got the tools that's definitely the way to go but if you don't use a "Dutch Key". Drill a hole anywhere on the line where a shaft and hub meet and thread it for a setscrew. Makes a pretty sturdy joint...
I think I am understanding you. Basically you're saying to drill the hole in the shaft to line up with the set screw of the hub then align the hub and use it to guide a tap so that I can put in a longer set screw and essentially use the setscrew as a key? That seems like a pretty smart idea.

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Old 06-15-2019, 10:12 PM
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Quote:
Originally Posted by o7oBaseMetal View Post
...I think I am understanding you. Basically you're saying to drill the hole in the shaft to line up with the set screw of the hub then align the hub and use it to guide a tap so that I can put in a longer set screw and essentially use the setscrew as a key? That seems like a pretty smart idea...
A Dutch Key has nothing to do with an existing set screw. You drill and tap the hole on the separation line of the parts and parallel to the centre line of the shaft. I made up a quick drawing to show the relationship of the parts. One of the advantages of a Dutch Key is that it can be in a blind hole...
Attached Files
File Type: pdf Dutch Key.pdf (5.8 KB, 32 views)
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