# Adjustable Chuck Stops For 3 and 4 Jaw Chucks - long post



## davidpbest (Aug 27, 2017)

This is not specific to Precision Matthews, so if this post belongs somewhere else on this site, let me know.

I decided I needed useful chuck stops for my PM1340 lathe.   I had tired of trying to use a pair of parallels to hold stock off the face of a chuck in bringing the stock to an appropriate height for machining where interference with the chuck jaws would create a problem.   

I decided to implement a set of adjustable height chuck stops for my two lathe chucks, and and another chuck I use in conjunction with my rotary table on the mill, but sometimes put on the lathe.   This documents the process, and is intended to assist any of you who might want to build adjustable height chuck stops. It is based, in part, on the design described in this video by Robin Renzetti:






This is what the result of my effort to implement something similar looks like once installed on a 3-jaw scroll chuck.







Here is how I approached the challenge of making these stops.  If you watch the video above, you'll notice that Robin makes the adjustable stops with an angled slot in the side for the clamping blocks to secure the stop.   This is what the profile looks like of the stops and their corresponding clamping block.






My first challenge was to figure out how to mill these profiles.   I wanted to mill up a few pieces of tool steel in these two profiles, each about 6-inches long, then later cut the profiled pieces into smaller components to finish the other milling operations (drilling, tapping, slotting, etc.).

I also wanted to be able to mill that angled slot using power feed on the X-axis, and since my mill (an RF45) doesn’t nod, but it does tilt, I decided to first machine up some soft jaws to hold the stock for the milling the profiles in 6-inch long sections along the X-axis travel of the mill.   Here is a drawing of the soft jaws I came up with and the sequence I used for milling the profiles of both the stop blocks and their clamping block counterparts.






And this is the result of using the soft jaws to profile the 5-degree tongue on the clamping block:






Once the profiles were machined it was a simple enough (although time consuming) operation to finish milling the various components.    Here is a drawing of the completed stops and clamping blocks for the 3-jaw chucks.  Note that there are two different versions of the stops – one for use when the jaws are facing outward, and another when the jaws are facing inward, but the same clamping block is used to secure either version.


Note that I used A2 tool steel for these components and used the Caswell black oxide and sealer on them once finished.   Also note that the adjustable height stop posts were made from partially threaded socket head cap screws, where I cut off the head and machined the hex male profile using a hex ER40 collet block on the mill.






To this point, the job followed pretty much what Robin had covered in his video (link above).








The 4-jaw chuck was a slightly different challenge, since I wanted to stops to be functional over the center hole in the chuck.    This is the design I came up with for these stops and clamping blocks – same as before, there are two versions of the stops: inward facing and outward facing.   On these, I decided to simplify the design by eliminating the clamping screw on each adjustable height stop post, and instead use thread-locking flat head screws for the adjustable height stops.






After machining all the parts (I thought this might never end), I used the Caswell black oxidizing and sealer system to protect the parts.   Here are most the parts (screws missing) after that process.






Here are a few pictures of how the 3-jaw versions came out and in use.
















And here are some pictures of the 4-jaw version in use.











If anyone wants to attempt this, the drawings for making all the versions and drilling the chucks to accept them are attached below in PDF format.  

There are also plenty of additional photos and lots of details on how I went about the machining of the stops here - I recommend you go through this album before attempting your own versions:   

https://flic.kr/s/aHsm7kJXwa

This was a fun project.   Hope this is useful to someone here.


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## Bob Korves (Aug 27, 2017)

David, your article references using A2 steel to make the parts.  Did you harden them?  Really nice work, by the way...


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## pstemari (Aug 27, 2017)

Nice!

What's your experience with the black "oxide" finish durability? The cold black finishes all seem to be selenium based, not an actual oxide finish, and it's not clear to me if they will actually hold up to shop use. 

Sent from my Pixel XL using Tapatalk


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## davidpbest (Aug 27, 2017)

pstemari said:


> Nice!
> 
> What's your experience with the black "oxide" finish durability? The cold black finishes all seem to be selenium based, not an actual oxide finish, and it's not clear to me if they will actually hold up to shop use.
> 
> Sent from my Pixel XL using Tapatalk



This is my first experience using the Caswell system.   Perhaps others can comment.


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## Alan H. (Aug 27, 2017)

Very well done David, thanks for sharing. 

As usual, you have been extremely kind in the extent and level of detail you have provided.


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## Bob Korves (Aug 27, 2017)

Duplicate post...


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## Janderso (Aug 18, 2020)

davidpbest said:


> This is not specific to Precision Matthews, so if this post belongs somewhere else on this site, let me know.
> 
> I decided I needed useful chuck stops for my PM1340 lathe.   I had tired of trying to use a pair of parallels to hold stock off the face of a chuck in bringing the stock to an appropriate height for machining where interference with the chuck jaws would create a problem.
> 
> ...


David,
I am no where near the machinist you are. If I had made them as precise and as well as you and Mr. Renzetti, I wouldn't have a problem.
It just seemed like a simple project. 
Maybe when I grow up, I'll try again using your design.
Really well done sir!!!!


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