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Now that @SeeMeCNC is selling thousands of Rostocks, they've focused on part/build uniformity. The QA challenge is uniformity across all variables.

Printing temps on the Onyx is different than printing on borosilicate glass - by about 10 degrees. Naturally, it's something you want to monitor/control.

Before I spend $50 bucks on a temp gun, I think I would prefer building something that affixes to the edge of the glass.

I was thinking of a thermister hooked up to an Arduino with an LED readout. The thermister could be affixed with RTV or perhaps even taking the aluminum part that holds the brass hot end and RTV'ing it to the glass.

Glass cooktops have a temp sensor. I've been looking for a part #/mfr but can't seem to find one.

Any thoughts? Even so, glass temps on the edges probably read differently than near the center.

John, your wording leads me to believe you've printed directly ON the Onyx PCB itself. THIS IS A VERY, VERY BAD THING. It's not designed for it and won't take it for long.

AFAIK, stoves use a thermocouple, not a thermistor. You can pick up a multi-meter that includes a thermistor probe from Harbor Freight pretty inexpensively.

Unless you're using an aluminum heat spreader, there's going to be a pretty steep temperature gradient from the center to the outside edge of the heated bed. I don't know how much of an actual problem this is - I've got a heat spreader on mine.

I print PLA at 55C with a 10:1 mix of water to Elmers White Glue applied to the glass. It works very, very well!

My heated bed won't reach anything higher than 90C as either my power supply or wiring is inadequate to the task. I'll know more about that once I've got my machine reassembled.

g.

I'm not sure a temperature gun will help you much.
Printing PLA directly on clean glass can be a complete crapshoot, it's heavily dependent on the plastic, bed and nozzle temperature, and no two plastics seem to like the same combination.
I've printed plenty of rolls of PLA that I cannot get to stick to plain glass effectively.
PVA glue is your friend for PLA, you can pretty much print on it cold if you raise the hotend temperature 10 or 20 degrees for the first layer.

Sorry, I am printing on glass w/glue.

I was hoping just to have a permanent display of the glass temp somewhere.

Do you know any good tricks for printing with ABS on the glass?

What issues are you having.
ABS won't stick to untreated glass at all, you need either Kapton, PET or Blue painters tape, or you can use an adhesive like hairspray or ABS juice (which is ABS disolved in acetone).
Run the bed between 80 and 110C, and print.
Hairspray is my current favorite, largely because it's convenient, I used ABS juice for a long time and it's hard to beat.

In combination with first layer temps and ABS juice, I've had pretty good luck. It's simple to do. Tiny pieces of abs into an ounce of acetone.

You drop a few drops on the glass in the area where you're printing and spread it out with stiff card stock (or at least that's what I use since I can just throw it away.)

When the surface gets too much glue or remains on it, take a razor at a low angle and smooth things down. If things get too uneven or built up, just take a paper towel, put some acetone on it and rub it clean.

An ounce of ABS Juice lasts for quite a few prints. I use a glass eye dropper with a rubber head. There are probably more scientific methods but for my measly prints, this works great!

(Ok, so now, will someone tell me how to very quickly come up to speed with a cad package for dummies?) LOL

Thanks guys - I'll give it a shot.

hand-held IR / laser pointer thermometers are about 10 bucks on dealextreme.com and ebay. Best 10 bucks I've ever spent!