Centering aid for polygonal stock

Centering polygonal stock in the 4jaw can be a trial. The centering should be done on the flat sides of the stock and not the corners. However, with the DI point bearing on the sides, one must be very careful to withdraw the DI plunger as the stock is rotated from side to side lest the plunger be 'caught' by a corner of the stock and bent, damaging the DI.

I use a dedicated DI mounted on a QCTP for aligning in the 4jaw. I simply slap it into position on the compound and the DI is automatically at center height.

To deal with the polygonal stock problem, I made a simple gizmo.

https://s3-us-west-1.amazonaws.com/f...he/36582-1.jpg

An aluminum rod clamps to the DI housing with a single setscrew. Attached to the bottom of this rod is an L-shaped piece of thin sheet steel that projects up in front of the DI plunger.

Now, as the polygonal stock is rotated, the stock corner contacts the sheet metal first and depresses the plunger as it passes, thus avoiding damage to the DI. A further advantage is that the motion of the sheet metal makes it obvious when the DI is perpendicular to the side of the stock - the position at which one wants to make the centering indication.

Thanks Marv! I've added your Centering Aid to our Measuring and Marking and Lathe Accessories categories, as well as to your builder page: mklotz's Homemade Tools. Your receipt:

<div id="blocks"> <div class="block b1 pngfix"> <div class="bimg"> <div> <a href="http://www.homemadetools.net/centering-aid"><img src="http://www.homemadetools.net/uploads/128226/centering-aid.jpeg" /></a></div> </div> <div class="head pngfix"></div> <div class="left pngfix"></div> <div class="right pngfix"></div> <div class="blockover b1 pngfix"> <div class="title"> <a href="http://www.homemadetools.net/centering-aid">Centering Aid</a> <span> by <a href="/builder/mklotz_3">mklotz</a></span> </div> <div class="tags">tags: <a href="http://www.homemadetools.net/tag/lathe">lathe</a>, <a href="http://www.homemadetools.net/tag/chuck">chuck</a>, <a href="http://www.homemadetools.net/tag/dial-indicator">dial indicator</a></div> </div> </div> </div>

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Originally Posted by mklotz

Centering square stock in the 4jaw can be a trial...To deal with the square stock problem, I made a simple gizmo.

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When not physically at a machine, I typically invest time in study of what work is coming up. Surfing the vast HMT content is more than entertainment.
Personally, tooling is a favored keystone to streamlining work. The 'cost' is high for the first article, diminishing with each produced. Upon re-use the cost is effectively zero.
Once again, [with equal thanks to HMT & mklotz] I have a solution for a run of link pins. Naturally, stocks larger than square collets available...Up to now, a square split bushing + 3 jaw was the only reasonable solution, and limited to one size!
Best part; they'll be concentric enough to drill for cotter pins clamped and located by the original material.
So, this accounts perfectly in my recurring "...this is not just a hobby" admonishment.

Thanks Marv, just starting to use a four jaw chuck, I need things like this.

Ralph

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Originally Posted by Ralphxyz

Thanks Marv, just starting to use a four jaw chuck, I need things like this.

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If you're new to the 4jaw, I strongly recommend you read my suggestions on centering...

http://www.homemadetools.net/forum/c...aw-chuck-27241

and this additional tip...

http://www.homemadetools.net/forum/4...3940#post79042

The 4jaw can be frustrating for newcomers to it but following those tips will ease the process considerably and make you as comfortable with it as you probably are already with the 3jaw.

Thanks, Marv. I try to keep your tips handy.

Ralph

Hi mklotz
Please forgive me if I am missing something here, but why clock a piece of hexagon bar in a 4-jaw chuck? Normally hexagon is used for making nuts and bolts and alike, so why use a four jaw when a 3-jaw self-centring chuck will hold on the flats of the bar and run true. I can understand, if a four jaw is the only chuck you have. Just interested as I have never seen this before and it seems a lot of effort to get a piece of hexagon to run true/concentric.
Thank you again for the posts you upload they are always interesting.
The Home Engineer

Quote:

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Originally Posted by thehomeengineer

Hi mklotz
Please forgive me if I am missing something here, but why clock a piece of hexagon bar in a 4-jaw chuck? Normally hexagon is used for making nuts and bolts and alike, so why use a four jaw when a 3-jaw self-centring chuck will hold on the flats of the bar and run true. I can understand, if a four jaw is the only chuck you have. Just interested as I have never seen this before and it seems a lot of effort to get a piece of hexagon to run true/concentric.
Thank you again for the posts you upload they are always interesting.

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The explanation is much simpler than one might expect.

The original picture showed a piece of square stock held in a V-block. During the recent PhotoSuckIt screw-up, that picture disappeared and I was forced to take a new photo to replace it. The original square chunk of metal had been used for a project and I was deeply immersed in the bookkeeping of restoring all my photos so I simply grabbed the first piece of polygonal stock that would present an edge to demonstrate the action of the flapper.

Yes, I would normally put hex stock in the 3jaw although one of my 4jaws is massive and a real beast to get on and off the lathe so I have used it for what would have been 3jaw jobs simply because I was too lazy to remove it.

Now that is what I call a real explanation!!

Thanks Marv

Hi mklotz
Thank you for the explanation all makes sense now.
I often put a 3-Jaw chuck into the massive 4-Jaw. As I cannot be bothered to get the crane to change the chuck. This is a common practice in the UK. This is also why the chuck keys are normally square on a 3-jaw and hexagon on a 4-jaw. Just put the hex one out of reach (in a cupboard) and then you can’t operate the wrong chuck and have the 3 jaw, job, etc. all crashing out of the 4-j. It is amazing how often you naturally go to the chuck that is, attached to the nose of the lathe spindle and not the one being held.
Thank you again
The Home Engineer
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3 Jaw in 4 Jaw now that is interesting, thank you!

Ralph

This method is great if your 3-Jaw chuck jaws are worn as you can true it up in the 4-Jaw so it again runs concentric once again.
But, I like this method for eccentric turning. When you have, several components all needing the same offset this can be achieved by adjusting the 4-Jaw to get the 3-Jaw to run out by the required throw/displacement and then each component can be put into the 3-jaw one after another knowing it has to be the same as the previous machined offset.
One note: when using a 4-Jaw you may need to slow the spindle RPM right down due to the eccentricity of the work. Larger chucks can have weights added as counter balances to overcome this issue.
The Home Engineer

Mounting a square collet block in the 4jaw or a hexagonal collet block in the 3jaw allows you to use collets without removing whatever chuck is mounted on the lathe.

This can be particularly handy when the work sequence demands going back and forth between the mill and the lathe.

Quote:

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Originally Posted by mklotz

Mounting a square collet block in the 4jaw or a hexagonal collet block in the 3jaw allows you to use collets without removing whatever chuck is mounted on the lathe.

This can be particularly handy when the work sequence demands going back and forth between the mill and the lathe.

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Marv, in order to remove/change the stock when using collet blocks you have to remove the collet block at least on the 5C collet block I just received. Mounting the 3 jaw chuck in the 4 jaw avoids this problem.

Possible you know of some other collet blocks?

Ralph

Marv, The Home Engineer and Ralph,

I added mandrel mountings to the back of a couple of my smaller 3-Jaw and 4-Jaw chucks for mounting into my larger 6-Jaw Adjust True chuck. I use the smaller chucks for holding diameters too small for the larger chucks (see http://www.homemadetools.net/forum/c...4848#post80696 and http://www.homemadetools.net/forum/c...0262#post72147 ). Another great technique is using a high precision ER32 collet chuck mounted in the 6-Jaw chuck for very precise 2nd operation work (see http://www.homemadetools.net/forum/e...aw-chuck-65548 ). The error in the chuck and collect chuck tend to cancel each other out within typically around 0.0002" to 0.0003" TIR depending on how much time you spend initially making the Adjust Tru adjustments to the 6-jaw chuck.

Regards,

Paul

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Originally Posted by Ralphxyz

Marv, in order to remove/change the stock when using collet blocks you have to remove the collet block at least on the 5C collet block I just received. Mounting the 3 jaw chuck in the 4 jaw avoids this problem.

Possible you know of some other collet blocks?

Ralph

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Collets can handle diameters far smaller than any lathe chuck can close to. If you're going to be doing a lot of collet swapping you really need to build a proper collet chuck for your lathe. That's what I did so the collet-block-in-chuck thing is only used very occasionally.

I have 5C collets and collet blocks but the block has to be removed from the chuck to change the workpiece.

I have ER25 collets that use a screw compression nut so these could be mounted in a 3 jaw chuck mounted in a 4 jaw chuck and multiple pieces could be turned
with the exact same placement easily, of course I do not have any ER25 collet blocks.

I guess once I learn how to cut threads and turn tapers I will have to make up collet blocks and nuts.

They are on ebay but kinda expensive for me.

Ralph

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Originally Posted by thehomeengineer

Hi mklotz
Thank you for the explanation all makes sense now.
I often put a 3-Jaw chuck into the massive 4-Jaw. As I cannot be bothered to get the crane to change the chuck. This is a common practice in the UK. This is also why the chuck keys are normally square on a 3-jaw and hexagon on a 4-jaw. Just put the hex one out of reach (in a cupboard) and then you can’t operate the wrong chuck and have the 3 jaw, job, etc. all crashing out of the 4-j. It is amazing how often you naturally go to the chuck that is, attached to the nose of the lathe spindle and not the one being held.
Thank you again
The Home Engineer
.

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At one employer, our 2 different 16" Clausings often held smaller 3 or 4 jaw chucks for precise reason Marv, thehomeengineer, and RalphXYZ observe. They had no 5C closers. Larger chuck capacity, means proportional increase in minimum size too...Even a passable 3 jaw can be clocked for better concentricity in a 4 jaw - provided the same key socket is used, consistent part size, and jaws are tightened in a uniform manner.
We made .250 and .400 ⌀ offset 'cams' periodically, combining a 3 and 4 jaw made it quick work.

This is slightly off-topic, but surprisingly (for me at least) hexagonal stock can be mounted in a 4 jaw self-centering chuck and remain centered with the lathe axis. No care need be taken about placement in the 4 jaw chuck. Try it if you have a self centering 4 jaw.
My "day to day" chuck is 200mm self centering because it affords better grip on the workpiece, AND it allows square and hexagonal stock to be mounted axially.