Jump to content
Sign in to follow this  
JAndrews

Cheap Pyrometer

Recommended Posts

You asked for it, so here it is! This is a super simple pyrometer for checking temperatures inside a forge, furnace, or crucible full of molten metal. Constructed with 1/2" metal conduit pipe. You will need 5/8" gouging rods from McMaster and will need a 12" long, 3/16" drill bit. VERY carefully drill the gouging rod down the middle of the rod, 11inches deep. These are fragile and break easy. The key to drilling it, is to start with a 3inch bit and be dead nuts straight and go slow. After you're in a couple inches, switch to the long bit. The thermocouple from McMaster will be contained in a ceramic shell and will be a tight fight inserting into the gouging rod. You might need to "wholler" out the hole carefully to get the rod fully inserted. After this is complete, mount the rod on the end of the conduit with some clamps.

Run Thermocouple wire down the tube and out the bottom some where. Connect it to your meter. What could be easier? I've seen guys pay upwards of $500 for a type K meter. This setup works probably just as good for a 1/10th the price. If It get's dropped, broke, or kicked, I'll only be torqued I have to drill another rod. If you find you are really good at drilling the carbon, drill yourself a few spares.

 

Parts list.... 1/4" probe Type K thermocouple, McMaster Carr, Part number 3859K44 (6bucks)

5/8" x 12"long Gouging carbons (I had a box of Blue Demons) McMaster-carr, part number should work 7979A18

Type K Thermocouple wire, 10ft. . McMaster Carr, part number 3870K35 (10bucks)

Cheapo type K meter off fleabay. (buy 1 and a spare) 5bucks each.

http://www.ebay.com/itm/Digital-LCD-Thermometer-Thermodetector-Meter-TM-902C-K-Type-Thermocouple-Probe-/261685822329?pt=LH_DefaultDomain_0&hash=item3cedb0c379

 

That's it. Your cheapo meter will come with a type k connector for the meter. Steal the little plug off it and stick it on your wire. Connect the wire to the Probe thats inserted into the rod and your done. These work on resistance. If ya can't wait for the slow boat from china on the meter, you can use a DVM and find yourself a chart. I personally like the chinese meter. It reads in C, but you can work out the conversion or make a chart. This very simple and LONG lasting cheapo setup could even be permanently installed in your forge. Dipping these rods into molten bronze wears them down a bit, but if you're just leaving it poked inside a forge, it could last for years.

 

Gouging rod next to Mcmaster car ceramic probe. Yup I broke some of the ceramic tube. No big deal

20150429_195230.jpg

 

Probe installed in the rod

20150429_195321.jpg

 

I welded a piece of the conduit on the end and split it longways, opened it up a bit and added clamps.

20150430_005859.jpg

 

Completed head

20161028_123523_resized.jpg

 

Meter.... Looks like it's about 75degrees in my garage. Not too shabby

20161028_123509.jpg

Edited by JAndrews

Share this post


Link to post
Share on other sites

Awesome! Thanks very much. I have a meter that reads in C and F, just been puttng off buying a probe til I get the sword forge done. Don't really need one for a coal forge, after all.

Share this post


Link to post
Share on other sites

I feel like I am missing something here. What is the purpose of the gouging rod? The ceramic sheath that you are putting through it is still exposed at the end, and is pretty much all the heat resistance I have found to be necessary.

Share this post


Link to post
Share on other sites

I bought a pyrometer and probe for about $80 if I remember right around 2011 or so; stainless steel probe and cheapo meter from ebay. The probe was a k type thermocouple from auberins maybe? The method described above seems very labor intensive and resource intensive.

Share this post


Link to post
Share on other sites

I think the reason for the gouging rod sheath is because he's dipping it into molten metal, a very corrosive thing to do. It's just a DIY graphite shield for the thermocouple probe, which is something I can use since the probe I have is not shielded at all. Plus it's cheaper than an inconel jacket!

Share this post


Link to post
Share on other sites

Just a heads-up on the TM902C pyrometers: I'd had about 30 or so that were boringly reliable and as accurate as big-name branded instruments costing more than ten times as much over the full range.

 

I bought another ten last year and put them on the shelf. They were bought on ebay and came from China.

 

Before I use one for the first time, I usually put it on the calibrator to check it is reading sensibly. I did this with several of the new batch and found they were all horribly inaccurate once the temperature got much above 800 degC (1472 degF).

 

Below that temperature, accuracy seemed pretty good; the variation was less than that I'd expect to see between different thermocouples, even those made to special limits of accuracy, but above 800 DegC, accuracy got progressively poorer and I was getting readings that were off by 80 DegC with the calibrator set at 1200 degC.

 

I still had a couple of the older ones and checked they were still reading correctly, mainly to check the calibrator. The old ones were fine.

 

There are some visible differences between the old ones and the new ones, but you've really got to have them side-by-side to see them.

Share this post


Link to post
Share on other sites

I think the reason for the gouging rod sheath is because he's dipping it into molten metal, a very corrosive thing to do. It's just a DIY graphite shield for the thermocouple probe, which is something I can use since the probe I have is not shielded at all. Plus it's cheaper than an inconel jacket!

 

But if the thermocouple tip is exposed the shield isn't shielding it.

 

So that is what my initial thought was. I now see that he isn't drilling all the way through the gouging rod, so the tip ISN'T exposed. That was the part I was missing. My mistake.

Share this post


Link to post
Share on other sites

No worries Jerrod, I leave about 3/4" of inch undrilled in the bottom of the rod. The rods do wear down with repeated dunks in bronze. Aluminum not so much. Just helps the probe live to fight another day when I break a rod. Still haven't bust one yet. (now I said it, I better start drilling another rod.... lol)

 

This isn't my creation by any means. The guys over at AA have many cheapo styles of this thing. My shop is where good tools go to die, so it needs to be cheap and easy.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...