Thread: Air Pencil Die Grinder Disappointment and Dilemma

Hi Bob,
I have not measured the run out on my grinder, but I can see it does have some, I did not expect it to be of a high standard especially as it is made China and the price. I did measure the shafts on the grinding stones and they are all over the place, some of mine will not fit fully into the collet others fall through. I have also received the four brass collets and just eyeballing them they seem to have some concentricity variations as well. Despite all of this I did set it up in the lathe and by rotating the tool in the collet managed to get it to run reasonable and faced a couple of end mills and it did a fairly good job of grinding them as long as you work within the torque limits of the tool.
Bob

Originally Posted by GTVi

I haven't received mine yet. I have received other things from HK, but no brass collets.

Unfortunately I don't have anything to measure run out (anyone can advise me on a good but cheap dial and stand ?), but I bought the CTC 4 bearing model for ~$70. Very happy with it so far.

Bill

Bill,

I have a thing about buying gear with someone else's name on it, I don't , but in the case of this tenth indicator, I got caught out. If you don't have a strong dislike for adorned tools and if you do have a use for it, it's yours for the cost of postage.
I can understand if you'd prefer something box fresh out of China. That understanding came about a couple of months ago.

The London made Baty is 40mm in diameter and functions flawlessly. The shaft will fit into a cheap Chinese magnetic stand clamp. Send me a PM if you are interested.

Bob.

Bob, I just bought one of those - mine is destined for a housing so I won't see any engraving (not to say that I may not grind it off) and the one I bought does not look to have anything engraved on it. Vintage Baty Shockproof DTI Dial Test Indicator Imperial 0001" D11 | eBay

If Bill is not interested I'm happy to swap with you - I need the flat back for my application and I think the glass on yours is cleaner so I can send the one I have to you and you can change the back over and the crystal (if you can) and I'll be happy. It will be a week or so before it gets here so time to consider.

Michael

Michael,

I'm trying to cull my collection, not maintain it! Bill's put his hand up for the adorned Baty.

Thank you for your kind offer.

Bob.

I am always available if anyone needs to find homes for excess dial indicators.

Dean

Originally Posted by Anorak Bob

I'm trying to cull my collection, not maintain it! .

Oh. Damn - does that mean all those Swiss pieces of equipment and accessories that I was wondering whether you would like I should offer to Stuart?

Originally Posted by Oldneweng

I am always available if anyone needs to find homes for excess dial indicators.

I'll bear you in mind if I have anything surplus to requirements

Michael

Originally Posted by Michael G

Oh. Damn - does that mean all those Swiss pieces of equipment and accessories that I was wondering whether you would like I should offer to Stuart?

Michael

MG, Don't bother Stu, he's busy with his optics. I'm sure I can clear some English stuff off a shelf to make space for another Swiss tidbit.

Originally Posted by 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?

Thanks for posting this Chris. I was looking at Suhner's site yesterday, not realising you had provided this link to a far more exhaustive catalogue than what I encountered. I'm wondering now if a flexible shaft electric pencil grinder might prove a better option. I looked at some Foredom grinders on Ebay and while they are expensive compared to the 30 dollar air pencils, they are about a third of the cost of the Swiss grinder.

A big plus for the electric version is a lack of noise. While the air pencil is not too bad, the compressor makes a hell of a racket. Knocks the idea of a bit of after hours grinding on the head.

BT

Originally Posted by Michael G

Oh. Damn - does that mean all those Swiss pieces of equipment and accessories that I was wondering whether you would like I should offer to Stuart?

Dont listen to him, thats exactly what he meant

Originally Posted by Anorak Bob

MG, Don't bother Stu, he's busy with his optics. I'm sure I can clear some English stuff off a shelf to make space for another Swiss tidbit.

You need to make a just a little more room already BT

Stuart

Well they finally arrived.

At the price I wasn't expecting too much, and I wasn't disappointed.

On the YJBC rating (You Just Bought Crap) they are up near the top.

I now know what that writing in red near the bottom of the ad was all about "notice:Actual size and measurements may have a little bit of a gap".

That is techno talk for " no two collets will have similar external dimensions". LOL.

But it wasn't a total failure as I intended to use these to compare Dremel collets to the air grinder ones and - yes they are quite different. So much so that they need to be reworked as I originally stated.

So I duly set about to rework the brass with a very small blade tool for brass. Bad move. The little collet went into self detruction mode - the brass seems pretty weak.

So I tried a fine pointed tool and that worked OK on the next one - success.

Well not quite. The next one of the four also suffered self destruction attack. Hmm, this looks bad, but then a brainwave.

Why not use a grinding/cutoff disc in the air grinder to gently reshape the tapers. HUGE SUCCESS. Did it in no time and it was near perfect.

So if you intend to try this, don't use a cutter, use the DG with a friction disc. This is the sort of work it excells at.

So I got 2 gooduns out of the 4. I drilled the two gooduns out larger and they work OK.

A few photo's below:

c1.jpgc2.jpg

I also drilled a couple of holes in the plastic case to take them.

c3.jpg

In addition to the tapers being wrong, the Dremel collets are an even more loose fit in the drive tube than the originals - way worse. The originals seem snug in comparison.

So the next step will be to make some steel collets from scratch and slot them with the air die grinder. Shouldn't be too hard.

See how we go

Cheers

Rob

Originally Posted by nearnexus

So the next step will be to make some steel collets from scratch and slot them with the air die grinder. Shouldn't be too hard.

I think you have nailed it with this suggestion. Perhaps heat treat them also.

After reading Bob "Anorak Bob" post with the run out he found with his two grinders I had a close look at mine today. They are not a precision tool. I found the spindle collet seat had .002" run out and was a bit roughly finished, I cleaned it up with a bit of 600 wet and dry paper. I then fitted the collet and inserted a ground 3mm diameter bar and took a reading about 10 mm in front of the collet nut it had .008" run out. I pulled it apart and took some measurements on the collet as I knew that it had two different diameters in it as some of the stone tools that came in the kit only just fit in while others slide right through. I found that the front of the collet where the three splits are had a 3.00mm bore, the last half had a 3.1mm bore. Spinning it by hand on the ground shaft it did not look like the outside diameter was concentric with the bore. I made up a close fitting stepped mandrel threaded on end and fitted the collet on to it in my ER32 chuck. A reading with the dial gauge confirmed that the bore and the outside were not concentric. Measuring inside the collet seat beyond the seat where the parallel part of the collet fits I found that this bore was a .005" larger in diameter than the parallel end of the collet. This resulted in the collet not seating, just floating.
I decided to take a skim cut .004" off the outside of the parallel part of the collet and turn up a close fitting bush one millimeter longer than the existing area and loctite it on. After it set up I turned it down to make it a snug fit in the chuck.A fair bit of fiddling but I ended up with a much smoother running tool. It now only has just under .002" run out on the ground bar out from the chuck. If any one has a collet with similar dimensions to mine ( this would be a miracle ) and would like to try out my little mandrel just let me know and I will post it off. A few photos to help clarify the above.
Bob

Thanks for the info Bob Krisfarm on the collet for the pencil grinder.
I received the brass ones yesterday & they are useless for this particular pencil grinder as they are of different dimensions.
I set up the $30 pencil grinder to check the run out with a dial gauge.
There was .003" runout on the taper, & .005" runout on the bore.
However when I inserted the mounted points supplied, fully down to the centre hole in the spindle of the machine & tightened the collet securely, the runout was .002" which for me was OK for the price of the tool.
My thoughts are, they have taken an easy way out in the manufacture of these machines & collets by providing location from the tapers on the collet & the slight taper on the end of the 3 mm dia spindle of the mounted point locating in the tapered centre hole of the main spindle of the machine. (can be seen with a strong torch with collet removed) This perhaps eliminates the need for an accurate mating of the parallel section of the collet, which just "floats"
Also checked with a .113" dia (no 33) twist drill & a .111" dia (no 34) twist drill & both ran true.
The dia of the shaft on the mounted points are .115" dia as supplied.
So my next job is to make a .125" dia collet for this machine to accept a lot of mounted points I have with this shaft dia.
Thanks Bob for the mandrel idea, I may use that for a final holding method when I make my 1/8" dia collet.
regards
Bruce

Originally Posted by Abratool

Thanks for the info Bob Krisfarm on the collet for the pencil grinder.
I received the brass ones yesterday & they are useless for this particular pencil grinder as they are of different dimensions.
I set up the $30 pencil grinder to check the run out with a dial gauge.
There was .003" runout on the taper, & .005" runout on the bore.
However when I inserted the mounted points supplied, fully down to the centre hole in the spindle of the machine & tightened the collet securely, the runout was .002" which for me was OK for the price of the tool.
My thoughts are, they have taken an easy way out in the manufacture of these machines & collets by providing location from the tapers on the collet & the slight taper on the end of the 3 mm dia spindle of the mounted point locating in the tapered centre hole of the main spindle of the machine. (can be seen with a strong torch with collet removed) This perhaps eliminates the need for an accurate mating of the parallel section of the collet, which just "floats"
Also checked with a .113" dia (no 33) twist drill & a .111" dia (no 34) twist drill & both ran true.
The dia of the shaft on the mounted points are .115" dia as supplied.
So my next job is to make a .125" dia collet for this machine to accept a lot of mounted points I have with this shaft dia.
Thanks Bob for the mandrel idea, I may use that for a final holding method when I make my 1/8" dia collet.
regards
Bruce

Photos of the set up I used.
regards
Bruce