Making a PID controller box for a 20lb melting pot

WobblyHand

WobblyHand

H-M Supporter - Diamond Member
H-M Lifetime Diamond Member
Joined
Dec 18, 2019
Messages
6,464
Recently bought a 20lb melting pot for casting lead. Had a lot of trouble maintaining the lead temperature for casting. So I decided to make a PID controller box for the Lee melting pot.

Bought a REXC100 PID controller kit, which included a solid state relay and a weird heat sink. Don't care for the heat sink really, it's adequate, but feels top heavy and strange to me. The kit also came with a type K thermocouple.

To house it all, I ended up getting a surplus ammo box. (100 rounds 50 cal) I will put in a fan on the solid state relay heat sink to keep it cool. Might not be necessary, but it will make me feel better.

The power cord come in from the back through a cable gland. The output of the SSR will be connected to a 110V power socket, where the lead pot plugs in. Also in the design is a power switch, a mini-circuit breaker, and a type K thermocouple socket. I designed this in FreeCAD. It's my best guess at how it will go together. The ammo box has a hinged lid, with a handle both of which are not yet shown. The entry and exit ports for the air will be screened to keep the whatever out. The model isn't quite complete, mostly because I don't know a few of the dimensions for the fan, and a couple other components.
isoview1c.jpg
The steel thickness is about 0.056". At this point, I'm not quite sure how to manage the big ~110mm holes in the steel. I am not fond of large hole saws, especially on sheet metal. Haven't seen any annular cutters that big, nor do I want to pay for one that size! I could always drill lots of holes, then file it. Could I use a boring head on a mill? Would I need to stuff the inside of the box with something to give the sheet metal some support?

Is there a way to get a hole saw to work? Found a 100 and 110mm hole saw for $30. How do you keep one of these from grabbing and throwing the box?
 
WobblyHand said:
The steel thickness is about 0.056". At this point, I'm not quite sure how to manage the big ~110mm holes in the steel. I am not fond of large hole saws, especially on sheet metal. Haven't seen any annular cutters that big, nor do I want to pay for one that size! I could always drill lots of holes, then file it. Could I use a boring head on a mill? Would I need to stuff the inside of the box with something to give the sheet metal some support?

Is there a way to get a hole saw to work? Found a 100 and 110mm hole saw for $30. How do you keep one of these from grabbing and throwing the box?
Click to expand...

I'd consider making a simple trepanning tool to cut the hole in sheet metal. You make a center to be held by the chuck, drill a cross hole with a set screw for the arm, and something pointy for the trepanation. It's like the boring head plan, except with a live tool center. Boring head would work too, just not as fast to set up.
 
pontiac428 said:
I'd consider making a simple trepanning tool to cut the hole in sheet metal. You make a center to be held by the chuck, drill a cross hole with a set screw for the arm, and something pointy for the trepanation. It's like the boring head plan, except with a live tool center. Boring head would work too, just not as fast to set up.
Click to expand...
Thanks for the idea. A 110mm hole would require about 80 RPM for an HSS cutter cutting steel. I don't know that my baby mill has the torque to run that low. On the other hand, it's only 0.055" stock. Is there any reason to have a center guide or bit?
 
Center point will make it fast to use by giving two points to measure for setting radius, and plunging into a pre-drilled center is faster than doing it centerless on a boring head.

Hole saws aren't round, and the multiple tooth tool points don't all follow the same path. Trepanning is a single point cut, like a laser in comparison.

I wonder about the use of the word, trepan. I thought it was specific to defining a center-anchored 3-point traverse to create an arc between a start and an end point. Running the tool as a circle cutter technically is a center-defined circle, not a trepan.
 
pontiac428 said:
Center point will make it fast to use by giving two points to measure for setting radius, and plunging into a pre-drilled center is faster than doing it centerless on a boring head.

Hole saws aren't round, and the multiple tooth tool points don't all follow the same path. Trepanning is a single point cut, like a laser in comparison.

I wonder about the use of the word, trepan. I thought it was specific to defining a center-anchored 3-point traverse to create an arc between a start and an end point. Running the tool as a circle cutter technically is a center-defined circle, not a trepan.
Click to expand...
That's good to know. I painfully know that hole saws aren't round and have bad run out. I'll try to make a tool to do this trepanning (or circle cutting).
 
WobblyHand said:
Interesting that two of those examples have the cutter the wrong way for a clean OD cut. Or am I mistaken?
Click to expand...
I agree, but this tool may also be used for o-ring grooving, which would require a wider cut.
 
I think I can make something like this. Pardon my design skills, still learning. Not going to draw a drill bit! Think I have everything I need to make it.
trepantool.jpg
Have some 1.25" 1144, and should be able to find some 5/8".
 
You must log in or register to reply here.
Back
Top