David Kahn

Help w/ Fisher Twin Screw Vise Repair

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I have a Fisher No. 6 (8.25 inch jaws) that has, alas, seen better days.  In particular, the upper screw, which is maybe 1.5 or 1.75 inches in diameter, is very badly worn.  Worse, the female part of the vise, where this upper threaded bar inserts, is also very badly worn.  The worn out male and female threads on the upper screw make the vise quite difficult to operate, such that it takes a great deal of effort to loosen or tighten the vise. 

It looks like, originally, the female threads were cut directly into the cast iron vise body.  There is no removable bearing or cartridge, which would facilitate repair.  To make matters worse, the threads on these screws are something like 3-threads-per-inch, which is beyond the capability of my modest SB 13 lathe.  (Not that I'd have any xxxxxxxx idea how to mount the vise body and recut cut the interior threads anyway.) 

Part of me wants to throw in the towel, as getting this thing working right doesn't seem like an easy project.  On the other hand, these big old Fisher vises are really cool, and I would love for there to be one more of them still working in the world.

It occurred to me that one option would be to bore the female threads out of the inside of the vise body, and then have the correct female threads cut into an appropriately sized length of schedule 40 steel pipe, which could then be brazed, or possibly pinned, into the bored-out vise.  Of course, I'd need to find a shop that could replicate the vise screw (the male piece) and cut matching interior threads on a piece of steel tubing/pipe.  I would guess this wouldn't be too difficult a task for a shop with a big lathe that is able to cut acme threads (or whatever xxx xxxx kind of threads Fisher used on these vises) at 3 tpi.  (Uninformed guesses being one of my specialties.)

Before diving in on something like this, I figured I should subject myself to public ridicule here.  Has anyone undertake a repair of this type before?  Any thoughts, wisdom, or suggestions?  Is there an easier or better way to go about this?  Can anyone recommend a competent, honest machine shop that might be willing to do the necessary machine work?  (Alternatively, does anyone have a NOS Fisher No. 6 vise laying around that they want to see in a good new home?)

Thanks much.

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I imagine having a machine shop make a new screw and screw nut, would cost more than the vise would be worth. I got a quote from my local machine shop for making a screw & screw box for an old leg vise and was told it would cost about $1000 U.S. to make. Needless to say that vise went in the metal pile to wait and see if I could find another vise with a good screw & screw box that had other damage and could be bought cheap.

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Don't bother with cutting custom screw threads.  Most don't know how to cut sq threads and though they are better  i believe Fisher used Acme threads anyhow. 

You can buy taps for threading but will cost you nearly what a new vise costs. 

The Fishers are neat because they don't use a spring for the return of the jaw.  this changes things.  

If you decide you want to throw in the towel I'd be interested in purchasing it.  I have a few projects like this on the burner for future uses. 

To make a screw box in Acme it's kind of tough to find wire with the taper.  It's one of the reasons sq threads are nice to repair. 

if both screws are junk it makes it even harder. 

here are a few rods I picked up for a vise project I have coming up. 

20191019_143933.jpg

You can purchase acme threaded rod from  sources.   Also can buy nuts. If you have the SB13 you can cut down to 4 threads per inch on the later models and 2 threads per inch on the earlier modes with the throw lever. 

I own a SB13X72.. 

Keystone threaded products is where I used to buy my threaded acme rod in stand sizes.  the 1.5" comes in 4 tpi. 

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Tough one. Unless you replace the bottom thread too, you need the exact thread. My plan would be to bore out both from the back, then turn down two acme coupling nuts to round on the outside,  but leave a .250 " shoulder at one end. 

Make a very light interference fit, cool the parts with dry ice and press them in from the back.

For this much work it should be economical enough to hire.

A good machine shop will ALWAYS price the work in advance, if not, go elsewhere.

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Aftist, I would do the opposite, Warm the vise and press the new nut in. Easier to keep a large part warmed up than keep a thin part cold. 

Shop it around. Are the threads ACME with a 29 degree taper, or are they 90 degree square threads?

How thick , and long, is the section around the threads in the leg?

I operate a gate valve at work that has a square thread on the opening mechanism. I have some large square threads on a piece that came off a crane. Old house jacks used square threads. So, you may be able to find the threads needed.

Shoot me the dimensions and I can see if the machine shop I was the tool maker for could knock it out. They have changed out some machines since I was there.

 

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18 hours ago, jlpservicesinc said:

Keystone threaded products is where I used to buy my threaded acme rod in stand sizes. 

Ooh, and they're within driving distance from me! Time to think seriously about replacing the busted-up screw on the Frankenvise!

(Also, I see from their website that they offer multiple thread starts on Acme threaded rod. Maybe the core of a homemade fly press...?)

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The website used to be awesome.  I used to order right off the site and actually could talk with someone if need be. 

It's totally different now. With submitting for a quote.  The listing of sizes with nuts and such was super handy. 

biggundr.  Nearly all the machinist I have spoken with in the last 30 years refuse to have anything to do with sq threads.  I have a lathe and info on how to do it but have never taken the time. 

I have rethreaded a thread box with new sq wire brazed in but it's on the list of things to do is cut some sq threads. 

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David, I have 2 #4 Fishers, and the threads are more complicated than the general consensus here believes. To my eye they have what looks like buttress rather than acme threads.  Additionally the direction of the butterss is reversed on the top and bottom screws.  Also, the diameter of the top screw is larger than the bottom screw, but they have the same lead.  Photos below are of one of mine, top screw first.  

If you replace one screw it is important that it have the same lead as the original or the "timing" chain will drive the two screws out of alignment and the vise will bind.  If yours is binding the first thing I would check is that the jaws are parallel and screws are indexed properly.  Pull off the chain and you can adjust each screw independently, then reinstall the chain.  

I'm an hour and a half from Lyme, but if you want to come over this way some time to look at mine, feel free to drop me a line.  

IMG_4138.thumb.JPG.f2efa4e829a0ca6f8a3dd464a79104b8.JPGIMG_4137.thumb.JPG.0a5303715a270531535396fd032692a1.JPG

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On 10/27/2019 at 4:09 PM, David Kahn said:

and then have the correct female threads cut into an appropriately sized length of schedule 40 steel pipe,

Sch 40 doesnt have the wall thickness for machining threads, plus the weld will just p!%& off the machinist.  Get some bushing stock.  

Crickets from the peanut gallery!

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Thanks very much Judson.  That is very helpful. 

I took a more careful look at the vise, and you are correct that the threads have a "buttress" shape.  Flat on the front, tapered on the back.  But only the top screw.  The bottom screw appears to be concentric, maybe just an acme thread?  Is this type of buttress thread a standard thread shape, or was it something proprietary to Fisher? 

It looks like the pitch on both threads is somewhere around 2.5 TPI. 

If I could find a machine shop in New England somewhere that could recut the top screw and a matching nut, I would love to do that.  Great point about pipe being the wrong material for a nut.  Given that it only needs to be four or five inches long, drilling out a piece of bar stock might be the way to go. 

Lastly, do you know what the correct process is for removing and/or replacing the chain on these vises?  Do you just torch heat the steel wrap on one of the links to open it and/or close it back up, or is there a trick?  The original chain, which is quite worn, appears to have cast links, and the only replacement chain I could find uses stamped steel instead. 

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What are the threads like in the box?  It the threads are worn in the vise. It will mean excelerated wear on the vise screw when replaced and binding as the screw and the threads have mated. 

If you really want to use this vise spending money on a threaded rod with the exact specs will be expensive unless you know someone who will do the work for low money. 

A buttress thread is just based on tool shape. as is acme as is square threads.   As long as you can get the thread pitch correct you should be all set. 

With this said. My lathe will only go as low as 4tpi  and wish I had the old box with 2tpi..  I looked into making a change gear to go to half speed but never had the need enough to really find exactly what I needed. 

There are 2 ways to do the chain.  Walk it off or undo the screws and the chain will slacken.. It just comes apart when you are past a certain point and can swivel it out. 

I have a machinist friend who might do it for little coin..   What is the OD, ID (depth of thread) and exact thread count?  I'll contact him and ask.  Also what material for the screw thread? 

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If the threads are not matching I would wonder about wear causing it or a previous replacement.

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17 hours ago, David Kahn said:

Do you just torch heat the steel wrap on one of the links to open it and/or close it back up, or is there a trick? 

That's what I did.  But if there is enough slack in the chain you can fold it to 90 degrees and slide the links apart.  Around here we call it "gutter chain" or "elevator chain"  for manure cleaners and hay elevators and you can find it at agriculture equipment dealers. 

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