Air Pencil Die Grinder Disappointment and Dilemma

[Anorak Bob]

Not wishing to upset the tone of Rob's pencil grinder thread I'll post my findings here. I had purchased a grinder for a cheap $31.49 from Ebay seller Melbourne Tools Shop and on delivery, found that the spindle did not rotate smoothly. It felt like there was grit in the bearings. I informed the seller of the problem and he promptly posted me a replacement grinder. The replacement grinder's spindle rotated in a somewhat smoother fashion but still stuck intermittently. Disappointing but nothing compared to when I measured the run out. The original grinder has .018" run out, the replacement, .0035".

Rob has shown via his videos, the versatility of these little grinders. My dilemma is who do I buy another grinder from? CTC have a very similar grinder, which suits mounting in a QCTP boring bar tool holder, for an additional 20 dollars. They also have a 4 bearing model for $64.11 (US?) shipped. Bit more fooling around fitting the latter in tool holder.

Has anyone checked the run out in their grinders? Richard "RC" has a 4 bearing CTC grinder, Bob "Krisfarm" and I think Bruce "Abratool" have both acquired grinders from Melbourne Tool. Has anyone bought one of the cheap CTC grinders?

The photos below probably don't mean much. If I worked out how to post a YouTube clip, all would be evident.

BT

ps. I did leave Joe at Melbourne Tools, positive feedback. My fault for buying Chinese.

[tanii51]

i got one too looks like my finger on the mouse going left click / up down wheel/ left click
when i get time ill try some other collets
john

[nearnexus]

Hi Bob,

In my web blog on these units I point out that runout is a fact of life with these units.

The cause as I see it is the rather basic collet design, and the loose fit necessary to avoid it becoming jammed in the collet tube.

As these spin at such high revolutions most runout is basically disguised in the grinding action, compared to say a slow moving cutter.

I will measure my CTC unit tomorrow but don't expect the readings to be any better than what you have.

Try reading off the collet tube rather than the tool piece and I expect runout will be less.

Rob

[.RC.]

run out on mine measures 0.07mm on some tools, 0.15mm on others...

[pipeclay]

As said earlier may be the better choice to measure the run out of the bore rather than the mounted point, then again if you dress the point it should run true.

Do these little grinders use vanes for drive, if so it may be the vane running on the barrel giving the grabbing feeling.

[Abratool]

As said earlier may be the better choice to measure the run out of the bore rather than the mounted point, then again if you dress the point it should run true.

Do these little grinders use vanes for drive, if so it may be the vane running on the barrel giving the grabbing feeling.

Peter
I mentioned the possible vane problem previously to Bob.
Sometimes this can happen. Perhaps Bob could run the grinder for a little while with some oil & if it is a minor interference fit with the vane length in the cylinder,rubbing on the end plates, it may fix itself.
Heres hoping.
I have not checked run out on my Melb grinder but will advise.
regards
Bruce

[Michael G]

These thing are only slim so the shaft would be even smaller in diameter - my first thought was when reading Bob's post was to wonder if the shaft had a slight bend in it. It would not take much if careless when applying preload to buckle a shaft I would have thought. Perhaps disassemble and then support the shaft at it's bearings and see what the run out is?

Michael

[Clubman7]

Just dress the grinding point when you fit it into the collet.
Only real drama is when you are using a rotary burr where it will cut on one side.

[Anorak Bob]

The "nose" is screwed very tightly into the red barrel. The whole assembly has a delicate feel to it and I'm afraid of crushing something. The little spanner supplied doesn't reach across to the other side of the nose which makes unscrewing the nose a touch trickier. I need to photograph the thing to illustrate the problem. It may prove worthwhile making a longer spanner.

The replacement grinder was both collet and nutless. Makes a comparison difficult. The collet I have doesn't smack of high precision but nearly 15 thou difference in runout between the two spindles suggests a problem elsewhere.

I'll have a go at measuring off the spindle collet seat tomorrow.

BT

[Abratool]

About the same time that I ordered the pencil grinder out of Melbourne, I placed the order for the 4 Brass collets out of Hong Kong, for the sum of $1.79 postage free.
Have not seen the Brass collets yet.
Has any one ever received these after ordering?
regards
Bruce
ps
Just measured the run out in the pencil grinder.
Its .005" at the collet nose & like Bobs its .018" at the abrasive mounted point.
I have got to stop buying "Crap"

[nearnexus]

Must be a hold up with the postage.

I've got those and three separate earlier items on order ex HK and haven't seen any of them.

One seller did warn me that there were current delays on the Chinese side of things.

Rob

[Oldneweng]

About the same time that I ordered the pencil grinder out of Melbourne, I placed the order for the 4 Brass collets out of Hong Kong, for the sum of $1.79 postage free.
Have not seen the Brass collets yet.
Has any one ever received these after ordering?
regards
Bruce
ps
Just measured the run out in the pencil grinder.
Its .005" at the collet nose & like Bobs its .018" at the abrasive mounted point.
I have got to stop buying "Crap"

Mine arrived Thursday (I think). They look ok. Four different sizes just like the set from dremel. I will try them today and check runout. I did find with my grinder that I needed to tighten the collet quite hard. I did it up pretty firm to make sure before using it as a test and then found it was still loose after I finished.

Dean

[cba_melbourne]

Suhner LSA81 Straight Pencil Grinder 0.1Hp, 80,000rpm (Rear Exhaust) - ARTCO - American Rotary Tools Company
The real thing is 15x the price, maybe one could be found second hand?

[nearnexus]

I went down the shed and tried to measure runout on the tool shaft and also the cone in the drive tube.

It's a bit of a pointless exercise as due to the loose fit of the basic collet in the drive tube, centering in the nose cap and drive tube cone can vary depending on how well the tool is aligned when tightened.

I doubt that a Dremel would be any different, given they both use the same system and require loose tolerance to avoid problems of the collet getting stuck in the tube and no way to remove it.

Rob

[Anorak Bob]

A bit more fiddling this afternoon.

I indicated off the spindle collet seat and the "old" grinder showed .003" TIR whilst its replacement fared better at .001" The seat in both grinders is rough. 20X magnification reveals a poor finish. That finish extends to the collet. I used a needle file to remove the burrs from the bore and from the slots but in all honesty I wasted my time. I turned a neat fitting brass shaft and mounting the collet on that shaft revealed that the collet bore is skewed. There is nearly.005" runout at the collet's nose and .002" at the opposite end.

For a tool with accessories that a seller can offer for less than 32 dollars with postage inclusive, expecting precision is extreme optimism. It will do for a bit of hand grinding.

BT