Modifying Standard 5-40 UNC countersunk cap head screws to suit Penn take-aparts

[Rothmar2]

Here's a little rainy day job you can do if you are so inclined, and have a mini lathe (or access to one).

Mike (mhc) had procured some  5-40 UNC x 1/4 Countersunk cap head screws from EBay, and asked me about modifying them for the lock ring screws on Jigmasters (and other take-apart Penn's). I think these particular ones are 304 stainless.

So I started off by removing a post/lock ring screw. Mike had sent me a corroded 501 post on request so I could mount the screws in my lathe's self centering chuck.





You can see that these screws sit proud of the lock ring and will interfere with the seating of the right side plate



There is approx 1mm difference in the screw head diameters





So we are going to skim down the heads to fit. First determine the depth of the bore in the chucking post



Then I cut a piece of 2.5mm welding rod slightly shorter than the bore depth. This will allow a few turns of thread to hold the screw, while the cut-off rod will give the screw end something to tighten against





Screw mounted on post. The drive key is 1/16 hex.



Mount the post in the chuck, and set a facing tool up on the tool-post. Take cuts from the centre-outwards. This will prevent material getting pushed into the drive cap, and clogging it. In fact, even going this way will still necessitate a little cleaning to get hex drive to fit. You can lightly tap the key in, or try cleaning the slot out with some wet/dry.



Face skim the head off a little at a time, check the OD of the head frequently.



Once close, touch the side of the tool against the head to remove the sharp edge. You can compare head diameter with an original slotted screw to see you're close.



And also smooth it off with some wet/dry.



Remove screw from chuck post and give it a test fit



Sa-weet!!!



Repeat for others. You can see these are a little shorter than the stock post screws, but are bang on for the seat screws.



So there you have it, upgrade your stock countersunk screws to SS!

[mhc]

Nice work Chris (again)
I would have preferred 316 but could only find 304 in Aus from Fastnerkitsonline.com.au. I know McMasters stock 316 screws in the USA but they don't ship internationally for whatever reason. I can get some longer screws next time - the one I measured must have been a stand screw in a post, it was 1/4 as well.

I had a go at a few by eye using a bench grinder and belt sander. I held them in an old post and rotated the head against the grinding wheel, keeping the direction of contact clockwise to stop it unscrewing - they ended up functional but not all the same height or entirely symmetrical.



 

Mike

[Alto Mare]

Beautiful job as always, Chris.
I want to thank you for giving me the idea of using a frame post, I never thought about it.
I was mounting the threaded side of the screw in the chuck, I now use a frame post.
No risk damaging the threads with this:

The screws on the right have the head reshaped and reduced in width, those are for side plates

It is very hard to get there, unless someone points you to the right direction
Thanks again Chris.

Sal

[Three se7ens]

Heres my method, but its a bit beyond the scope of most.  ER collets can clamp tight without crushing threads, because of the large surface area of the collets.  ER16 is pictured, and goes up to 10mm.  The benefit is this method is that you can cut without risk of the screw backing out. 

[Rothmar2]

No problem Sal, glad to have helped. As I've said before, if a post I put up helps just one person, it's been worth the time and effort to post.
The Collets Adam have shown are the nuts for mounting small screws, if I had access to a set of collets, that would have been the way I would have gone.