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Thread: Lee 4-20 Pot modification

  1. #1
    Boolit Buddy Tmaloy's Avatar
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    Lee 4-20 Pot modification

    I was hoping to start this on a positive note, but alas somethings don't come to plan when you want them too. Too start, I have been casting over a dutch oven and propane burner since I learned from some of my now deceased friends who first taught me the art of casting over 30 years ago. I recently decided to go modern so to speak and wanted to get an electric pot with PID contoller. Contacted HATCH for the PID, done. Ordered the NOE mold guide and bracket for the Lee, done. Found a Lee 4-20 pot on eBay for $60.55 with free shipping. (Sweet deal!) Went to the PO to pick up the pot. Looked a bit odd as I noticed the package came from Brownells. Opened the box and found out the pot was a 220V model. To sum up I am working with the seller to correct the issue as they even admitted they sent the wrong item.

    Now, on to the mod part, I decided since I already opened the box, I would take some measurements for a modification I have been thinking about after reading some of the complaints of the Lee pot. The biggest being the amount of leaking that occurs, second was the instability and weak point of the valve pour assembly. Mainly stepping in with the issue that constant use of the lifting up and down of the valve would eventually loosen or cause the #6 shoulder screws to come loose from either the top or bottom. I originally posted a mockup of what I thought would work in the "Fixing the Lee Drip-O-Matic" post.

    Click image for larger version. 

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    I had some time to run to the hardware store, since the wife said she need a few things to make dinner. Went browsing around the nuts and bolt section. I took a 6" 6-32 threaded rod, and then went to the cubby that had the threaded aluminum 6-32 threaded spacers. Found a 1/2" and 1" X1/4" diameter, looked at the springs around there too. Found I think a #126 compression spring. Went back to the fasteners and found the brass 6-32 thumbscrews and a couple of #6 fender washers. Went and got the wife's wants and headed home.

    Got the Lee pot and mocked it up from the outside, looked like I can make this work. If only I got the right Lee pot.....I could take it apart and get going! While looking at the pot I got, I noticed that the factory shoulder bolt on top was crooked, played with it a bit and noticed it would bind during operation. Okay, so I figured the little assortment of nuts and threaded rod would keep the alignment better than those screws. Below is the hardware that I will be using once I get the pot I was supposed to get. The only modification to the valve bar handle would be to drill out the guide holes to 1/4" and use some sprue lube on it to make it smoother. Bear in mind that I may even go bigger and use 8-32 in the future maybe if I actually get to disassemble the pot and need to give it a little more strength if the need arises.

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    Just to note, when I do get the right pot, I do intend to lap the valve and pour spout and mount the thermocouple in the bottom of the pot. Thanks to HATCH for making his PID controller, Drew P, for the TC mounting idea, Lathesmith for a custom piece I'm hoping he can turn for me, and the rest of the CB members for their input and knowledge.

    Tmaloy

  2. #2
    Boolit Master
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    Looking forward to seeing this project in action, some great ideas here. Regards Stephen

  3. #3
    Boolit Buddy metricmonkeywrench's Avatar
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    Just curious on what the effect of the heat of the pot ledge on the spring will be...

  4. #4
    AKA: GRMPS Conditor22's Avatar
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    Looks like a good idea
    The rod should thread all the way thru.
    Observation, the handle needs to slide up and down the bottom of the rod
    how well will the handle slide on the all-thread
    you could substitute a lead weight on a sleeve w/o the top nut for the spring.

  5. #5
    Boolit Buddy Tmaloy's Avatar
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    To answer some questions, metricmonkeywrench the spring on the ledge will be one of those wait and see deals.

    Conditor22 the bottom part also has a spacer for the valve assembly to ride on. Also I have asked Lathesmith to turn a 1" X 3" piece of brass stock that will thread on to the valve rod and that will add the weight to it.

    Sent from my SM-G950F using Tapatalk
    Last edited by Tmaloy; 07-10-2019 at 01:43 PM.

  6. #6
    Boolit Master RED BEAR's Avatar
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    Please keep us informed very interested.

  7. #7
    Boolit Buddy Sig556r's Avatar
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    Watching too...

  8. #8
    Boolit Master



    retread's Avatar
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    I like your approach to the problems. I am constantly tightening the shoulder bots on my two 4-20s. The spring pressure would be the key, to heavy and it would be tiring when lifting for casting, too little and it would not seat firmly enough. I think if it were adjustable with the nut on the top (is it?), that would solve that problem. Good thinking! Thanks for the post.

  9. #9
    Boolit Buddy Tmaloy's Avatar
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    retread the 6" threaded rod has enough length on it where the nut and spacer could be adjusted some. Food for thought.

    Sent from my SM-G950F using Tapatalk

  10. #10
    Boolit Buddy Tmaloy's Avatar
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    So I pulled the pot that I am disputing and thought I could give more detailed information for the modification. After looking it over the bottom spacer would be a 1/4" with the thumbnut. The top with the spring would probably have less compression to hold the the valve arm down with the 1" spacer. I bought a 3/4" spacer and that has some downward tension when used with the spring. Pic has the assembly mocked up against the valve arm assembly. Just a reminder drilling out the valve arm to acommodate the 1/4" diameter threaded spacers used will be required so the spacers will slide through. Sprue lube would be a good one to use there.

    Click image for larger version. 

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    Like was mentioned before, when the valve arm assembly is lifted on this pot to pour, it will bind up and stick at the top of the stroke. Pic shows the shoulder bolt and the leaning tower it makes. I peeked in to look at the tip of the valve and the pour spout and saw how misaligned they were due to how the crooked shoulder bolt was when actuating. This maybe a big reason why the pot leaks and Lee recommends twisting the valve down when it leaks to apply pressure to the valve rod, hopefully an aligned assembly will get it done and keeps the leaks out. Just to note, I would have to nudge the handle down, I can only imagine if this pot was fully loaded with alloy.

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    Update. While updating this post, I checked my ebay messages and the seller gave me a full refund, if I'm lucky they may let me get the pot for free due to their error and time wasted. If they ask for it back, I will send it. If not, I will just order a 110V heating element from Lee and bypass the factory thermostat. (Fingers crossed, Thanks for the tip HATCH) So I will update when I get a line on a new pot or get this one working if need be. Also, Lathesmith will be will be turning a brass handle that I will thread on to the valve rod so I can adjust by gloved hand and add some weight to it to help prevent leaks. I think I should start working out.

    Stay tuned CB members!

  11. #11
    Boolit Buddy
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    I did something similar on mine. I added a spring on the top that helps add presssure on the rod preventing leaks in between pours. Works better than original but not 100%. I polished it and cleaned the orifice too. I think these pots were just destined to drip.

  12. #12
    Boolit Buddy Tmaloy's Avatar
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    Quote Originally Posted by psychbiker View Post
    I did something similar on mine. I added a spring on the top that helps add presssure on the rod preventing leaks in between pours. Works better than original but not 100%. I polished it and cleaned the orifice too. I think these pots were just destined to drip.
    I hope to try and minimize the leaks from the Lee pot with the modifications I am planning. If all goes well, I will make sure to note my path to it. I also just checked the Brownells website, they have the Lee 4-20 pot on sale for $63.99 and I used a promo code for free shipping. I hope to have it some time next week and get everything together.

  13. #13
    AKA: GRMPS Conditor22's Avatar
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    Killer deal with free shipping code "VB5"

    I'd suggest shortening the FE3463 8–32x1 Carriage Bolt that attaches EM1120 Valve Knob to EL3426 Valve Arm Assembly so you lift up straighter.

    I'd put a piece of thick leather or 1/4 plywood between the valve knob and valve arm assembly IF you're worried about the heat.


  14. #14
    Boolit Master Idz's Avatar
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    Hoping not to jinx me, but I've never had a problem with the lee 20lb pot in 1000s of casts. Maybe its just luck or the few things I do differently. I don't fiddle with pot until the lead is completely melted and ready to cast and then spin the valve rod a couple of times like Lee recommends. I use soft range lead so I don't dump in flux and corrode everything. I allow the natural crust to develop over the melted lead to isolate it from the air. I run the temperature just above the lead melting point, about 5 on the the thermostat. I don't know if this is why I have no problem or its just dumb luck.

  15. #15
    Boolit Buddy Tmaloy's Avatar
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    Conditor22, I was thinking of using a shorter carriage bolt. I may try it just to see how it does, I always cast with gloves so the heat may not be an issue.

    Idz, glad your pot is working great for you. I like to tinker and if the modifications help others, It feels good if it helps others.

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BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check