Classic cars forum & vehicle restoration.

[Glenn Crawford]

I don't normally give up - but I give up!

I have been given a secondhand sand blasting cabinet, a big steel box on legs with two holes in the front door (with gauntlets attached) so you can hold the workpiece and blasting gun. There's a window in the front, and a light inside. The floor of the work space is a grille, under which is a hopper containing the abrasive grit. The blasting gun is like the head of a paint sprayer, but instead of a paint canister it has a broad tube whcih dips down into a pickup buried in the grit. It's a properly made thing - not home made. The cabinet came with various buckets of different grades of grit.

This is all fine, except I can't make it work. Air rushes through but it won't pick up any grit. I have thoroughly cleaned right through; changed my new (120psi/8 bar) compressor for one with a higher pressure (150psi/10 bar); tried all the different grades of grit; tried all three of the nozzles supplied. Except for an occasional and rare brief rush of abrasive through the nozzle, all I get is lots of air!

I have spent hours on this. Someone out there knows the answer. Help please!

[Rick]

I've got a smaller version that sits on top of a workbench and it seems to work as intended - is the grit you're using perfectly dry? I did have problems with a different type of sandblaster once when the grit was a little damp and it clogged things up continually. So long as the pickup pipe is buried under the mound of grit in the bottom of your unit, I can't see why it wouldn't work, unless there are some air leaks in the pickup or gun?

R
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[Glenn Crawford]

No leaks - but the grit is of unknown age. It doesn't feel or act damp, which is to say it pours like table salt does, but is that a good enough test?

[Rick]

sounds like it should be ok then - any leaks on the air line running from the compressor to the cabinet?

R
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[Glenn Crawford]

No, everything is airtight. The compressor is connected to the cabinet via a self-coiling airline. Inside the cabinet there's just an on/off valve with the blasting gun attached to the outlet - it looks like it's always been there, and is needed as there's no on/off trigger on the gun itself.

I wonder whether the airline needs to be a bigger bore, or not a self-coiling type, to avoid pressure drop along the way? Does this sound feasible?

[Uncle Joe]

Due to the fact that I have a warped sense of humour, this topic amuses me......

UJ

[buzzy bee]

Hi

What size is your hose?

Cheers

Dave

[Glenn Crawford]

The air fittings are all ¼" BSP (standard garage and machine shop fitments) and the airline has them crimped on to either end. The inside of the coiled airline itself... duhhh... sorry, without cutting it open I can't tell, probably around ¼" / 6mm. I have an alternative (reinforced rubber) line which I have tried, it made no difference at all to the sand blaster, though it too was probably ¼" internal bore.

[buzzy bee]

Hi

I would have thought that was big enough, may be wrong though.

Cheers

Dave

[Glenn Crawford]

I've just been to the workshop, and I took a photo of the infernal machine: unfortunately I've just discovered that I can't include a photo in postings to this forum! I did measure tha air hose though and can confirm that it's 10mm outside diameter and therefore probably 6mm / ¼" bore. I'll try buying a bigger bore hose, in case it's an air flow issue, unless anyone's got a better idea?

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[UKdave2002]

Every problem I have ever had with blast cleaning was due to the grit being damp, If poss put some in your kitchen oven for an hour on the lowest temperature, and try it again. It really does make a big difference when the grit is bone dry.

Dave

[Glenn Crawford]

Thanks for the suggestions: still no joy. I dried the sand in the oven at home, and it's definitely dry (a fine dust emerges when I pour it); I fitted a larger-diameter air hose, 8mm bore, to minimise pressure drop. Still nothing; no sand at all, zilch. There is certainly some suction at the end of the hose which dips into the sand - I checked - but not enough to lift the sand up the tube. So I think the air flow rate is too low - perhaps there's some sort of restrictor in my compressor outlet and I'm going to attack that next week!

[oldgoaly]

Second hand sand blast cabinets, blasting media should be used, sand can casue respritory problems. clean out all the hoses and pick-up tubes, flakes or larger chunks of rust can find there way into the system. The blaster gun, has 2 wear peices one is the nozzle, larger the hole more air it takes! second is the venturii inside the gun when this wear out it does not pick up sand properly. Moisture is always a propblem, compressor piping can help reduce problems here is a link to a sandblast cabinet maker http://www.tptools.com/lp2/Tech_Notes.html they some helpful info. I got mine the guy said it used to work great, well the turned the media into a powder, went thru and cleaned replaced wear parts, and yes it works like new! Also i made a plastic sheild for my window, held in by magnets, i can remove and clean so it easy to see what i'm doing. Good luck with you blaster! Take care

[buzzy bee]

Hi

I have just remembered one thing I did encounter once, the nozzle or the feed from the pickup was some real hard material ceramic, or something really hard. I remember having to drill this section out, this was on a new blaster as the hols did not go all of the way through, drilling was hard work, a fair few drill bits were used, but it made all the difference and it actually worked. So work checking that?

Cheers

Dave

[oldgoaly]

http://www.davepropst.com/Article/Art5/Article5.htm take a look at Dave's cabinet. He also has some neat other tools and projects. The Hydraulic press is new, Dave told me the 4 by 4 forum had been rough on him, guess he didn't make use of part from an old 4 x 4 or use the frame off the old double wide out back(a redneck thing) Take care! tt