Soft jaws for holding long pipe

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Harold_V
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Soft jaws for holding long pipe

Post by Harold_V »

I was asked by jcfx (one of our readers) to provide information in regards to the building of the soft jaws I used for holding 4" schedule 40 pipe for machining. https://www.chaski.org/homemachinist/vi ... 4&t=109989

I prepared the jaws without thinking of posting, so I have no pictures of the process involved, but it should be quite obvious to those with an interest in making a set. I do have some pictures of the finished jaws, and that should help.

A few years ago Patio, one of our readers and my good friend, gave me a couple weights from a weight machine such as those found at the gym. Made of mild steel, there is a reasonable amount of usable material in each, and as luck would have it, they are wide enough to make soft jaws for my chuck. The material is 1" thick, and three inches tall. I cut the necessary lengths from the short weight in the picture.

DSC00056.JPG

With three pieces sawn to the desired thickness, I began the process by squaring the material, and then cutting each to a common height. The 1" thickness was acceptable for the width of the jaws, as was the 3" width of material acceptable for the length of the jaws, so all I had to do was square the two sawn faces and make them parallel with one another. I size the height according to the screws used, ensuring that there is enough material to allow a full depth counterbore for the head, and enough material remaining beneath the counterbores for secure holding with an adequate number of threads engaged with the master jaws. Each case will have its own requirements, so one fits them to their chuck according to the discovered dimensions.

With the jaws squared and cut to size, the next operation was to machine the long slot, which I hoped to have in the center of each jaw. The slots were roughed on all three, then the finish cuts were taken to make them a snug slip fit with the master jaws of the chuck. This operation is done by using an undersized end mill, and moving the saddle of the mill. Careful measurement permits keeping the slot on center, as well as on size. I used a carbide end mill for this operation, as speeds and feeds can be improved considerably, with an improved surface finish.

With the long slots created, I then set a stop in my vise, so I could replace each jaw and keep register. That's quite important when you have more than one item to machine, or when you must remove an item from the holding device and reinstall it, even if there's just one piece. I located center by picking up the stopped edge, then moved to the appropriate location and roughed each of the jaw inserts. Once roughed, they were then taken to size, with a snug slip fit to the locating key, which is removable from the master jaws.

With the slots finished, the last machining operation before welding was to drill the holes and counterbore each hole to fit the socket head caps screws. For this operation, the same setup was used as was used for the short slot. As everything was equal distant from each end, and as the material was identical from jaw to jaw, I was able to locate the first hole, then to simply rotate the piece 180° in the vise for the second hole. With the jaws located on narrow parallels, I was able to drill through without interference. Rather than make changes of the center drill (or starter drill) and other tools, I simply rotated each jaw, performing the same operation on all six holes before progressing to the next operation. By doing so, you can make a stop setup for depth and have all holes turn out the same. With the holes drilled and counterbored, they were then deburred with a 90° countersink, again with a stop set. When finished, because the setup permitted rotating the jaws for the drilling operation, they were then turned upside down so the exit of the two holes could be deburred, again using a 90° countersink.

DSC00060.JPG

With the jaw bases now machined, it was time to make the gussets. The jaws themselves were left over from a similar set I had built many years ago. I had removed them from the base, so the base could be used for other purposes, thinking that I'd most likely never need them again. I was well pleased that I had the presence of mind to not discard them.

The first time they were used I had installed a single gusset, which made it less then convenient to install the one screw. I decided that it would be in my best interest to avoid that this time, so I settled on a pair of thin gussets, one on each side of the jaw. They were sawn from some scrap material (I don't discard anything), then milled for uniformity. An attempt at uniformity was the reason for machining, as it's always a good idea to try to keep soft jaws in reasonable balance, although in this instance it would be highly unlikely that the jaws would see high speed service.

With the gussets machined, it was time to assemble the jaws. I used simple spacers to locate each component so they could be tacked (I used TIG to do the welding). With all of the pieces firmly tacked in place, the jaws were then welded. When cool, the radii on the gussets was created with my 6" x 48" belt sander, then the jaws were subjected to the blast cabinet so they'd have a uniform appearance.

With the blasting finished, the jaws were installed in the chuck, and a spider used to set them so a skim cut of the bore would create a firm seating area. You may notice that the jaws were not machined fully, just wide enough so they'd support the pipe. No sense removing material unnecessarily for no gain. By carefully choosing the spider size, one can fit jaws to a part without removing a large amount of material. That allows soft jaws to be used far more times than if one is careless. When jaws are as demanding of so much time to make, that is a serious consideration.

DSC00058.JPG
DSC00059.JPG

I'm pleased to report that the soft jaws worked extremely well. When working with pipe, there's huge amount of internal stress that is released as surfaces are machined, so it's asking a lot for a piece to be turned on one end, then turned 180° for the opposite end to be machined, but soft jaws make that task quite easy. For the intended purpose, it might be acceptable to pronounce a perfect result, as I was able to turn and bore the 9" length of 4" schedule 40 pipe without issue, with a very respectable match line in the center.

I think this is enough information for anyone to duplicate the results. if, however, you have any questions, feel free to ask. I'll do my best to provide answers.

H
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Russ Hanscom
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Re: Soft jaws for holding long pipe

Post by Russ Hanscom »

Very nice indeed.

Patio must go to a different gym; all of the weights I have run across were made of plastic coated concrete or mystery metal full of hard spots.
John Hasler
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Re: Soft jaws for holding long pipe

Post by John Hasler »

Russ Hanscom wrote: Mon Nov 02, 2020 9:06 am Very nice indeed.

Patio must go to a different gym; all of the weights I have run across were made of plastic coated concrete or mystery metal full of hard spots.
I had some once that were plastic shells filled with shot.

However, a couple of years ago I bought some 45 lb weights for $10 each at the local university surplus store. They were cast iron with the name of the university cast into them and made of pretty good grey iron. I've made several parts such as the base for my rotary table out of them and still have quite a bit left. Quite uniform and workable. Of course, they were probably made in a foundry in Eau Claire...
jcfx
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Re: Soft jaws for holding long pipe

Post by jcfx »

Harold, thanks for the write up, my questions are when you set the pre load with the spider
to do your boring I'm assuming that you're gripping with the inner most part of the jaw 'insert" ?
I've attached a pic with the area circled in red .
Harold_pipe_jaws.jpg
And the curved parts of the jaws were made from a larger pipe with a suitable wall thickness ?
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Harold_V
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Re: Soft jaws for holding long pipe

Post by Harold_V »

jcfx wrote: Mon Nov 02, 2020 6:24 pm Harold, thanks for the write up, my questions are when you set the pre load with the spider
to do your boring I'm assuming that you're gripping with the inner most part of the jaw 'insert" ?
Correct, but keep in mind that your ultimate purpose is to duplicate the pressure the jaws see in use, so you want the spider located as far from the scroll as you can get it, yet still have clearance for machining in the proximity of the spider, assuming that's necessary. The idea is to load the jaws such that they spread at the outward end as much as the (jaw) slide allows. If you get too close to the scroll, you can have issues with concentricity and parallelism of the jaws. Not common, but I've experienced that problem.
And the curved parts of the jaws were made from a larger pipe with a suitable wall thickness ?
Heh! They were made more than 50 years ago, but it's safe to say that they were likely made from heavy wall tubing of some description. It's obvious to me that I had tried to increase the radius of the jaws, as they show signs of having been beaten with a hammer along their length. I likely heated the material so it would move a little. I don't remember what I did, however.

It's a good idea to use material that is similar in profile to the item you intend to grip, so you don't have to machine away excessive material, reducing the useful life of the jaws, plus thinning them in areas where you may need strength.

H
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RSG
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Re: Soft jaws for holding long pipe

Post by RSG »

Well done Harold.....rather elaborately fabricated but necessary for the application or I know you wouldn't have gone to such great lengths with the welding and all.

You've mentioned in the past of the "spiders" you use to load the jaws as having three screws that can be adjusted accordingly. FWIW I thought I would share my version of how I deal with pre-load as most of my requirements are far too small to have such a device as your "spider" fit inside the jaws. I've developed a series of discs and rods that start at .125" and go up in 1/16" increments to as large as 2.5" in dia. I always try to use the largest dia disc I can to minimise jaw loss while preparing them to receive the part. They are quick and stack up nicely on the shelf.

Oh, and my softjaw collection is one of those things you mentioned in your post where "you don't discard of anything" 8)
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Harold_V
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Re: Soft jaws for holding long pipe

Post by Harold_V »

RSG wrote: Tue Nov 03, 2020 7:47 am I know you wouldn't have gone to such great lengths with the welding and all.
Yeah, that's true, and my perspective is far different from the guy who is trying to make a living. What's important to me is that what ever I do works. If it takes an unreasonable amount of time, that doesn't prevent me from getting it done.
You've mentioned in the past of the "spiders" you use to load the jaws as having three screws that can be adjusted accordingly. FWIW I thought I would share my version of how I deal with pre-load as most of my requirements are far too small to have such a device as your "spider" fit inside the jaws. I've developed a series of discs and rods that start at .125" and go up in 1/16" increments to as large as 2.5" in dia. I always try to use the largest dia disc I can to minimise jaw loss while preparing them to receive the part. They are quick and stack up nicely on the shelf.
I've had a tendency to avoid using soft jaws for small work, so I use my Hardinge-Sjogren collet chuck instead. If I have to work with a bastard size, I'll choose a collet that is slightly larger than the piece to be held, and turn and bore a thin wall bushing that fits the part(s). I don't even split the bushing, so long as the parts are identical in size. If I must have a horizontal stop, I use one that installs in the spindle. I try to avoid using stops that install in the collet itself, as they are diameter sensitive, meaning that if the piece one grips varies from part to part, the linear dimension varies accordingly. The positive stop I use prevents that, so you can hold extremely tight tolerance without issue.

Anyway, the point is that you've addressed the issue very nicely. The only thing I'd do differently is to accumulate a collection in smaller increments of change. I generally set a size that demands just a few thou to be removed from the jaws when they are machined. I'll make small adjustments more than once if necessary, as the time it takes is far less than the time it takes to make a new set of jaws.

H
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Mr Ron
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Re: Soft jaws for holding long pipe

Post by Mr Ron »

I find it easier to turn a wood plug for the PVC pipe. That keeps the pipe from being distorted. When done, just reverse the plug and finish the other end. With a plug in both ends, it can be held at both ends in the lathe.
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Russ Hanscom
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Re: Soft jaws for holding long pipe

Post by Russ Hanscom »

true, but a wood plug will not work for steel, or if you need to bore the inside.
bill jones
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Re: Soft jaws for holding long pipe

Post by bill jones »

---here is a set my long jaws for dealing with tubing
long aluminum soft jaws of sleeves and large tubing.JPG
---made this set specifically for shortening automotive engine cylinder bore sleeves---that typically need to be shortened about .600" or so

---they also work for doing holding some large diameter stuff
large tubing mounted on long sft jaws.JPG

---I left a short locating edge at the far left end of the jaws to help square up the large tube
locating edge at left side---closeup.JPG

---this sort of shows the inside of the jaws and the allen bolts used for attaching to the two piece lathe jaws
Attachments
large tubing is faced off.JPG
Russ Hanscom
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Re: Soft jaws for holding long pipe

Post by Russ Hanscom »

Very nice, simple too.
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Harold_V
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Re: Soft jaws for holding long pipe

Post by Harold_V »

Yep! Very nice.
I like wider jaws so there's little or no distortion of the gripped item, but for facing, that setup is outstanding. Makes no difference to the facing cut.

The takeaway that is hoped for with this thread is that there's a good and reliable way to grip long, thin items, a way that, more or less, guarantees a good outcome.

Once made, a set of jaws like those shown in this thread (not just mine) are invaluable.

Soft jaws---the magic bullet of lathe holding.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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