# Switching from 3 jaw to 4 jaw chuck



## mriplaybass (Jun 17, 2020)

OK, so I am just about to head out into uncharted territory, and start my first simple project. I thought that I had pretty well figured out what I needed to do, but all came to a screeching halt. I want to turn part of a 1" piece of bar stock down so that it will look like an old fashion square head bolt. I'm so proud of myself knowing that I needed to change over to a 4 jaw chuck to turn square stock.  I removed the 3 jaw and prepared to install the 4 jaw when I discovered that the 3 jaw had a bigger threaded diameter than the 4 jaw. I looked among the many different parts that the previous owner included, and found the correct sized back plate. Problem is, the chuck has 4 mounting holes and the back plate only has 3! Upon further exploration, I see that there is an adapter on the head stock which I would assume if removed, would expose the correct diameter for the 4 jaw chuck. But I can't get it off!!  There are 3 holes drilled around the shoulder of the adapter that look like some sort of spanner wrench with round pegs might fit into. Am I on the right track? and how do I know what type of wrench to get?


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## markba633csi (Jun 17, 2020)

OK, try this:  First, apply a liberal amount of penetrating solvent like liquid wrench or homemade juice such as 50/50 acetone/ATF
Wrap a couple layers of cardboard on the assembly and secure with a large hose clamp.  Using channel-locks or vise grips, try to remove the adapter. You might have success whapping on the grips with a 2X4 if firm tugs don't do it. I hesitate to recommend engaging the backgears since gear teeth can be broken.  Wedging a piece of wood or a rag into the pulleys is a less risky way to immobilize the spindle. A bit of heat might help, but be careful of fire. Use a light bulb or stick a soldering iron in the spindle.  Be patient, it may take extended soaking over a couple days
-Mark


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## mikey (Jun 17, 2020)

Measure the ID of the holes. The spanner you use must have a pin that will fit in the holes so they are called Pin Spanner Wrenches. Personally, I prefer hinged pin spanners as opposed to the rigid ones. Looks like this one.


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## mickri (Jun 17, 2020)

I have a similar adapter that I made for one of my chucks.  It can be a pain to get off.  I now put anti seize on the threads whenever I use it.  If you can't wait to get a correct size spanner wrench you could sacrifice one of the holes.  First like suggested above apply liberal doses of your favorite  penetrating solvent and let it soak over night.  Put something that fits in the hole 




and give it a good whack with a hammer right next to the adapter.  





 One good wack is better that a bunch of lighter taps.  You will have to hold the pin when you wack it.  Not enough hands to show that in the picture.  And don't have the back gears engaged.  You could break some of the teeth.


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## mriplaybass (Jun 18, 2020)

Thanks for the ideas. I tried a strap wrench, that didn't work. Tried the punch in the hole whacking it with a hammer........broke the punch! I didn't try the hose clamp since the strap wrench didn't work, but I did soak it over night with PB Blaster. 
I ended up making this: 




Two hits with a hammer and it came right off!
But now I have hit a wall with my project. I don't think that the previous owner ever used the 4 jaw chuck. The threads on the back plate don't match the spindle. Guess I'll be watching eBay!


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## JimDawson (Jun 18, 2020)

mriplaybass said:


> The threads on the back plate don't match the spindle.



Time to make another adapter.


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## mriplaybass (Jun 19, 2020)

That's a bit advanced for me. I am still learning what all the levers and cranks do. Plus, this lathe is the only precision machine that I currently have, so I am pretty much forced into looking for a pre made one that fits. Is there a number based on diameter and thread pitch? or do I just look for one based on spindle diameter and thread pitch along with spacing of the 4 bolts that hold it to the chuck?


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## mickri (Jun 19, 2020)

Making an adapter is not that difficult.  I am a newbie at this hobby too and have made two adapters so far.  One that I call a chuck for my ER32 collets and the other shown in the pictures posted above was for a 4 chuck.

What type of lathe do you have?  That will help people to give you suggestions.

Both of my adapters were made using a 3 jaw chuck.   The operations involve basic turning and boring to diameters and external and internal threading.  When I was learning how to operate my lathe I used PVC pipe to practice on.  Then progressed to ordinary steel pipe.  The diameters that you turn to and the thread pitch are not important.  You are just learning the motions and getting used to your lathe.

When you get to making the adapter you will need to measure the threads and the OD on the lathe spindle and the threads and ID on the chuck.  This will determine what diameters you have to turn and bore to and the thread TPI that you have to cut.  Here is a link the my thread on making the adapter for the 4 jaw chuck.  https://www.hobby-machinist.com/threads/chuck-adapter-backing-plate.81042/  It should help you out on making an adapter.

Have fun with your project.


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## mriplaybass (Jun 19, 2020)

Good thread mickri. My 4 jaw chuck is not threaded, and relies on an adapter which threads to the spindle and is held to the chuck with four 7/16" bolts. I worry about being able to drill these holes symmetrically given that I do not have a mill or any other precision drilling machines. I tried to do some threading, and was very pleased that I set out to cut 20tpi, and actually achieved that. But all that showed me was that I was able to figure out the lathes settings. I did not even use a bit ground for threading. I only cut in far enough to see if it would match my thread gauge. I do not yet know how to cut the large threads that the spindle has, or what kind of bit to use to make the very coarse threads. I have not yet attempted to grind any of my own bits. If I am measuring correctly, it looks like 7tpi is what I am going to have to cut. The lathe is a Hamilton. 15x32


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## Twirpunky (Jun 19, 2020)

mriplaybass said:


> . I want to turn part of a 1" piece of bar stock down so that it will look like an old fashion square head bolt. I'm so proud of myself knowing that I needed to change over to a 4 jaw chuck to turn square stock.


 
    You do need a 4 jaw for lots of work. Good practice to use it.

  Here is a better and faster way to make square head bolts that look like old ones.

   1. Heat up the head of a standard bolt (until red) that has the size and thread you already need. (Even lag bolts) Hang on to it with tongs or vice grip by the thread.
   2.  If you have an anvil, use it.  If not, clamp a piece of heavy steel in your vice and position the head bolt horizontally on the flat surface with one of the points up and the other point on the flat surface.
   3.  Whak with hammer to flatten the top and bottom points.
   4. Rotate 90 degrees and whak some more until you have a square.
   5. Repeat step 4 until you have the size of square you want.
   6.  Drill a hole in a heavy piece of flat stock steel the size of the bolt you are making. (threaded portion)
   7.  Put your squared bolt in the hole all the way to the head and reheat the head.
   8. Hit the head of the bolt with angle blows 4 times. One time on each square side of the head at an angle.  This will give you a Pyramid looking top with a square head bolt.
   9. Wire brush while still hot.

  I do some ornamental Iron working as a hobby and have made at least a hundred of square bolts like this.

D


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## markba633csi (Jun 19, 2020)

Usually, the backplate fit is not determined by the mounting bolts but instead, by a rim or shoulder that fits the plate to the chuck.
Therefore, the mounting bolt holes in the plate can be oversize or even slotted
Look for a pre-threaded blank backplate that fits your spindle then fit it to the chuck. Take another close look at your spindle so you know for sure what the thread is- 7 tpi sounds odd- could it actually be 8?
-Mark
PS good job on the wrench tool


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## mickri (Jun 19, 2020)

The bolts only hold the adapter to the chuck.  There should be what is sometimes referred to as a register on the chuck that the adapter fits into.  This is a precise fit and is what keeps the chuck concentric with the spindle bore.  Not the bolts.  You don't need a mill or a precise drilling machine to drill the holes for the bolts.  A drill press will work just fine.  You might even be able to drill the holes with a hand drill using the chuck as a guide.  To locate the holes for the bolts it would be nice to have a set of transfer punches.  $10 or so from Harbor Freight.  Transfer punches are really handy to have.  You will use them often.  The people who are really good at machining can transfer punch all 4 holes in one go.  For us mere mortals I find it best to do one hole first.  Bolt the adapter to the chuck and then transfer punch the remaining 3 holes.

If you haven't read it yet Mikey's very long thread on grinding tool bits will clue you in to everything you need to know on how to grind tool bits.  https://www.hobby-machinist.com/threads/models-for-grinding-hss-lathe-tools.62111/  It is worth the time to read it.  I have read it several times.

Post a picture of the back of the chuck.  Even chucks/backing plates/adapters with threads have a register.


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## mriplaybass (Jun 20, 2020)

I am turning down a piece of 1 1/2" square stock. One end will retain the square shape in order to fit a wrench to it. the other end will be bored out and fitted with a pin to connect it to a shaft. So I don't need to make a square shape.

When I removed the backing plate from the chuck, I realized the the plate was indexed (registered) to the chuck. I'm not totally sure about the thread count. I only laid a ruller on the threads, and counted the high points of the thread. Could be 8.

With all the work that I do in my shop, mostly automotive, I can't believe that I have never heard of transfer punches! Those things are greater than sliced bread! All these years I have been transfering holes using my brad point cobalt drill bits. Gotta get some of those!

My next dilema is finding some 5 1/4" diameter steel bar. I just called the local steel yard, who sells all their steel by the foot if you don't need an entire 20' piece. $123.00 for one ft.! Guess I'll be watching Craig's list and Facebook market place for steel, or just looking for a used adapter with the correct threads that I can modify the register to fit my chuck.





4 jaw is on the left


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## mickri (Jun 20, 2020)

You might try contacting the machine shops in your area.  They usually have scrap pieces left over from jobs.  They might have what you need.  I typically pay $0.50 per pound for scrap.  I would also ask the steel yard who they may have sold some 5 1/4 bar to.  That shop might have some scrap pieces.  Speedy Metals sells by the inch.  Shipping can be expensive.  https://www.speedymetals.com/p-727-5-14-rd-cold-finished-1018.aspx

From looking at the picture of the chuck on the left it looks like it is threaded.  Have you measured those threads and the ID? The picture you posted of the spindle still has the adapter on it that you have removed.  Have you measured the threads on the spindle and the OD of the spindle?  If you don't have thread gauges you should get both imperial and metric.  The gauges are dirt cheap and you will need them.


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## mriplaybass (Jun 20, 2020)

Good idea! I didn't think of calling machine or fab shops to see if they have any small scrap pieces. I'll give that a try Monday. The picture of the 4 jaw chuck has the adapter that it came with setting on it. The chuck itself has no threads. I'm guessing that it is somewhere around 10 to 12tpi. Definitely not the threads on the spindle. The adapter that is on the spindle is for the 3 jaw. The adapter shown goes from 2 1/4 up to 2 3/4. I assume that I would want to make or buy a back plate that would thread to the spindle itself and not to another adapter.


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## mickri (Jun 20, 2020)

You want to make a backing plate that screws onto the spindle and is a very good fit into the chuck.  Basically identical to the existing backing plate but threaded to fit onto the spindle.  You may get lucky here.  First what is the OD of the register portion of the spindle and what is the OD and TPI  on the threaded portion of the spindle.  The OD of the threaded portion of the spindle may be smaller than the OD of the register portion of the spindle.  I ran into this on the adapter that I made.  Now if the threaded portion of the existing backing plate has a smaller ID than the OD of the spindle threads you may be able to bore out and thread the existing backing plate to fit.  You will need to compare the major and minor diameters of the threads and the TPI on the spindle and the backing plate.  It would be really nice if the spindle and the backing plate have the same TPI.


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## Jimsehr (Jun 20, 2020)

mriplaybass said:


> OK, so I am just about to head out into uncharted territory, and start my first simple project. I thought that I had pretty well figured out what I needed to do, but all came to a screeching halt. I want to turn part of a 1" piece of bar stock down so that it will look like an old fashion square head bolt. I'm so proud of myself knowing that I needed to change over to a 4 jaw chuck to turn square stock.  I removed the 3 jaw and prepared to install the 4 jaw when I discovered that the 3 jaw had a bigger threaded diameter than the 4 jaw. I looked among the many different parts that the previous owner included, and found the correct sized back plate. Problem is, the chuck has 4 mounting holes and the back plate only has 3! Upon further exploration, I see that there is an adapter on the head stock which I would assume if removed, would expose the correct diameter for the 4 jaw chuck. But I can't get it off!!  There are 3 holes drilled around the shoulder of the adapter that look like some sort of spanner wrench with round pegs might fit into. Am I on the right track? and how do I know what type of wrench to get?



Amazon , sells square head bolts If you want to buy them.

 Jimsehr


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## mriplaybass (Feb 11, 2021)

Fast forward 8 months. I have been gone or otherwise unable to spend much time learning about my lathe. About 4 weeks ago, I decided to continue trying to learn what's what on the lathe before I forget what I have already learned.
After learning more about the lathe's controls, I decided to try to make some shock absorber studs that fit on the U bolt skid plates on my off road Jeep. I bent one of them pretty badly running the Rubicon Trail last September.
Not exactly rocket science, but I did manage to figure out how to face, turn a diameter, turn to a shoulder, and cut 2 different threads, and diameters. 




OK, enough of my self proclaimed atta boys.
As I stated above, I need to make a backing plate for my 4 jaw chuck, and I think that I am ready to try it. My actual question to all of you is, do I have to make it out of cast iron? or can I use cold rolled steel? I have not had much luck finding either at a reasonable price, so I hope to narrow the selection of material down so I don't have to waste time looking at the wrong thing.


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## neilkingent (Feb 11, 2021)

go to Shars and order a back plate

Sent from my SM-N975U using Tapatalk


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## mriplaybass (Feb 12, 2021)

neilkingent said:


> go to Shars and order a back plate
> 
> Sent from my SM-N975U using Tapatalk


Wow! Great place for tooling! Thanks! Unfortunately, nothing that will fit my lathe that I can see. The only back plates that I can find with 6TPI are ones with a 2 3/8" spindle diameter. Mine is 2 1/4" x 6TPI.
The 4 jaw chuck is 9", but the existing back plate is only 5.325" diameter with a 4.719" register. I guess that I could cut the diameter to whatever I need, but the 2 3/8" diameter for the spindle is too big.
I did find a guy on Facebook market place near me who will cut some 5 1/2" bar for me and sell it by the pound. The current back plate is 2 1/2" deep. So I figure that I will buy a piece somewhere in the 5" to 8" range. That way I can mess 1 or 2 of them up. He is offering 12L14, or 4140HT for the same price. Which one would be best for this project? I know that 4140HT is harder. I do have both HSS and carbide bits.


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## mriplaybass (Mar 2, 2021)

Anyone?


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## DavidR8 (Mar 2, 2021)

What's the make and model of your lathe?


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## mriplaybass (Mar 3, 2021)

It's a Hamilton 14". Not sure of the model#. The spindle is a 2 1/4" x 6TPI. There is also an adapter for the 3 jaw chuck which increases the spindle to 2 3/4" x 6TPI, so either would work for me. I have looked at Shars, and several other places, and no one has a back plate that will fit.


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## DavidR8 (Mar 3, 2021)

What if you bought a 2.25x8 TPI backplate and bored and threaded it for 2.75x6 TPI?


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## mriplaybass (Mar 3, 2021)

I've thought about doing that, but for what it would cost me for a 2.25x8 back plate that I would basically have to completely remake from scratch to get it to my specs, not to mention, I would only have one chance to get it right, I can purchase enough round stock to make 9 adapters. Being a complete novice, I kind of figure that I'm going to mess up at least the first one or two attempts. I talked with the guy who has the bar stock to see if he has any round cast bars, but he doesn't. All that he has is 12L14 or 4140HT. He says that the 12L14 is easier to machine, so I am guessing that would be the better choice for my application. I assume that this is a softer metal, and would be less like to gall the threads on my spindle.


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## DavidR8 (Mar 3, 2021)

12L14 has lead added to the mix, hence the "L". It is really nice to machine. 

Making a plate from flat stock is fair bit of machining so lots of practice. I'd suggest practising threading both external and internal to get familiar with the dance steps.


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## mriplaybass (Mar 3, 2021)

I have figured out how to thread. As a matter of fact, I have made several parts for my off road Jeep. Haven't done much internal threading though. I just bought some PVC pipe to practice on.


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## Tozguy (Mar 3, 2021)

mriplaybass said:


> My next dilema is finding some 5 1/4" diameter steel bar. I just called the local steel yard, who sells all their steel by the foot if you don't need an entire 20' piece. $123.00 for one ft.!


That happened to me with our local steel supplier. I told them that I only needed a short piece and asked if they knew of anyone locally that could accommodate me. They gave me the name of one of their customers, a welding shop, and sure enough the owner of the welding shop cut me exactly what I needed. Of course it was not free but very reasonable (if you show up when they are not too busy or can wait until they can get to it). But steel is getting expensive any way you look at it.


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