2017 POTD Thread Archive

[Franko]

Thanks for all your help and the very generous offer, Will. This has all been very educational. (I love this forum!)

I think I can replace components but my fear is that some may be damaged or malfunctioning that show no physical evidence. It is possible I can find how to check a mosfet and capacitor on the Googles with a multimeter. If I get stuck, I may take you up on your offer.

I think it is time to return this item to its regularly scheduled programming. Thanks Will, Roy, Jeff. You guys are great!

 

[Martin W]

Not really machining related but I did use my mill to mill the rivets out. Helped my son change lower control arm bushings and ball joints on his Chevy HHR. Easy job turned harder when one bolt on the control arm, nut was spinning inside the frame. Could not see it or even get a wrench in. I was able to feel it turn with my finger , so I put my finger in to line up the nut and then stuck my mig gun where my finger was and gave it about 5 seconds of weld. Bolt backed right out. Then it was the stubborn rivets on the ball joints.
Was a good day. Got to spend an afternoon with my son. He learned its not always as easy as YouTube makes it look.
Martin W

 

[JimDawson]

An update on the sandblaster: http://www.hobby-machinist.com/thre...in-your-shop-today.14637/page-324#post-483748

After 8 mind numbing hours of sandblasting , I have to say that the modifications were successful. The sand flow is good, but don't overfill the hopper. Too much sand affects the flow. The last time I did this job I had to rent a diesel powered, 185 CFM construction compressor because I was using so much air my compressor couldn't keep up. Now my 5hp compressor keeps up just fine running at half speed. The compressor runs continuously and maintains 110 PSI. Running continuously is not a bad thing, it is really better for the system than cycling. Uses less power, and doesn't stress the components like the centrifugal switch and start capacitor in the motor.

Why is the compressor running at half speed you ask? Well because some idiot (me) ordered a 1725 RPM replacement motor instead of a 3450 RPM motor. Actually it keeps up with my shop air needs with no problem. But for this job I would like a bit more pressure, about 125 would be just right. I haven't put my other compressor on line yet, but it will have a VFD on it to run the 3 phase motor, so for sandblasting I can adjust the air delivery rate.

The new window is starting to etch a bit after 8 hours of use. My son suggested putting a screen in place to protect the window. I'm going to order some 200 mesh stainless screen and see how that works out. 70 mesh media and a 200 mesh screen should be a good combination. The new LED lamp is great, plenty of light, worth the money.

 

[ch2co]

What are you guys using for blasting media?

 

[JimDawson]

What are you guys using for blasting media?

I'm using Black Aluminum Oxide, 70 grit. From Harbor Freight

 

[whitmore]

Franco
You might think of sending that bad board to someone that you know thats good at electronics and let them troubleshoot it (and repair it?)

I second this: if it blows fuses, it isn't the fancy digital gizmo that
you need a diagnostic wizard to repair, but the honkin thick-wires power handling
parts (usually, rectifier, filter, or switch transistor), which are relatively easy
to inspect/replace. And, even with a stiff labor charge, a fraction of the
$300 price tag for board-replace.

The board-replace is an OK solution for warranty coverage, and turns
into a cash cow for the manufacturer after warranty is up, so the
price is usually high (and sadly, the availability not).

 

[DHarris]

Just my .02, but the black "short" from the cap to the connection point looks like the capacitor (it appears to be an electrolytic type of cap) "blew" from short / over current and they then "outgas" thru a internal pressure relief that always seems to be on the bottom (dumb design IMO). So cap needs to be replaced too - but it will not be the cause of the failure, just one of the collateral damaged parts.

 

[FOMOGO]

I use glass bead in mine and the and the viewing port glass is original, and still clear after 15 yrs of pretty hard use. It's a little larger than yours, but i doubt that should make much difference. Are you using a Vacuum on it? For the first few yrs I used clear peal off vinyl sheets over the glass, but found they really weren't necessary. I'm thinking the glass in mine is tempered and that's the difference. Nice job on the feed modification. Mike

I'm using Black Aluminum Oxide, 70 grit. From Harbor Freight

 

[whitmore]

Just my .02, but the black "short" from the cap to the connection point looks like the capacitor (it appears to be an electrolytic type of cap) "blew" from short / over current and they then "outgas" ...not be the cause of the failure, just one of the collateral damaged parts.

That can be checked; if the black mark is soot, it will come off with a pencil
eraser. If it's a carbonized track on the board, it won't.

The scorched IR2013 chips may have been killed by bad MOSFETs,
in which case there may be bad resistors connected to the IR2013 pin 5 and pin 7,
the gate drive resistors. Any bad gate drive resistors might indicate that
the associated MOSFET...melted down.

So, the bill of materials now is three capacitors, three IR2013 gate drivers,
and up to six MOSFETs and six surface-mount gate resistors. Lots of collateral
damage; and on the picture, doesn't D301 look a bit scarred?

 

[JimDawson]

Are you using a Vacuum on it?

Yes, I hook my shopvac to it. Maybe tempered glass would be better. I don't think that glass beads are as quite as hard on the glass as an abrasive media. I remember many years ago we had a blast cabinet in the shop I worked at, ran only glass beads. I don't remember the glass frosting.