Is it my tube or my power supply?

[fred ungewitter]

Symptom: reduced speed required to cut 3 mm plywood at full (safe) power 65% on 60 watt tube

When I replaced the original tube, 2 1/2 years ago, I got a genuine 60 watt model, 1200 mm long 55 mm diameter. It's difficult to recall for certain, but I believe I was cutting 3 mm ply at 20 mm per second. Last night's project requires the same 65% but the speed is now down to 3 mm / second and it doesn't cut all the way through.

I've replaced my ammeter because I suspected the power indications were incorrect on the old gauge, but the new gauge is still showing much lower current than expected for 65% power.

Will a slowly failing tube also show incorrect current figures on the meter?

Do power supplies fail gradually in the manner noted? The speed change has been very gradual, enough so that I'd been blaming my memory for not recalling the correct burn settings, but it's gone well beyond that.

Replacing the power supply and the tube together is more expensive than one or the other, obviously. I'd like to get it correct on the first attempt.

[Gene Uselman]

You have of course already checked the beam alignments to be sure they are optimum? If the current is lower than it used to be I would look first to the power supply. The percentage of power used is a fluid thing, depending upon the power supply and how well it is matched to the tube.

[fred ungewitter]

I apologize for omitting that aspect. At the beginning of this recognition of power loss, when the travel speed had to drop below 15 mm / sec, I performed a mirror and lens cleaning and alignment. Apparently, I'm getting better at that, because all nine points of the test burn were within a millimeter of the center of the pattern. It's rather satisfying to see one burn after another on the mirror test pieces to be so close as to be indistinguishable.

Also in the middle of this project of correction, I used Russ' doohickey and collected settings that were inconsistent with those from the period of time after receiving the gadget.

It's encouraging to hear that it may be the power supply, as that's the lower cost item of the two.

I've found the best price for an MYJG-60W from Cloudray on eBay with free shipping. The dimensions are a bit different from mine, but that could be my rough measuring as they are close. It also appears to be a plug-swap for the wiring, a bonus. New Jersey source means no waiting weeks for the boat. If it turns out that it's the tube, at least I'll have a fresh power supply in the machine.

[fred ungewitter]

The power supply arrived yesterday, and it's a near perfect match. The only aspects that are different are the missing 110v/220v switch (dedicated 110v) and an RJ-45 jack adjacent to the connector bus. It has me curious, but there was no manual to let me know what the RJ-45 jack can do.

My settings (perf mode on) have gone from 3 mm /sec at 65 percent power to 20 mm / sec on 3 mm birch ply and up to 30 mm / sec with perf mode off.

I'd forgotten just how fast this thing was, since it deteriorated so slowly.

I have yet to re-test power settings with the DooHickey. I had previously determined that 28 ma was the max, but the 65 percent now uses only about 16 ma.

Does that mean I can run my tube at a higher power setting as long as I don't go above the 28 ma specified for this length and diameter?

[Gene Uselman]

Yep- the power percent curve will be different for sure. Work up to your max current for a max power % and then back off to where ever you are comfortable.

[Doug Fisher]

>>My settings (perf mode on)<<

This is a great mode for cutting some materials that don't react well to normal laser cutting mode. I use it for some thin part cutting. With that said, I have read this mode is very hard on power supplies. I guess you have to look at it as a cost of doing business.

[fred ungewitter]

I wondered about the aspect of constantly cycling the laser tube to get perf mode. It does a great job of providing a clean plywood edge, but I'm no longer happy with that option if it means replacing the power supply every few years!