Dremel as toolpost grinder.

[TXFred]

I'm seeking feedback from anyone who has used one of these tools in this manner.

My ideal tool would be a flex shaft that I could mount to a quick change toolpost. My 20 year old Craftsman would be perfect since it fits a 1/2" boring bar holder. Unfortunately it's got 0.0055" of side play due to being 20 years old.

Specifically, is there a model of tool out there that is known for having minimal amounts of spindle runout and side play?

Cheers,
Frederic

[mcarvey]

I've done the Dremel flex shaft thing before, and although it sort of works, I've found a better way. There are all sorts of problems with the flex shaft- the bearings aren't that rigid, there is a bunch of runout, it uses a little 3 jaw chuck thing that increases runout even more, it takes 10 minutes to attach (and then remove) from your dremel, the dremel has poor control of speed, low torque, etc.
I've found a much better way to do it. Get a Proxxon 38481, a 20mm shaft collar from McMaster (p/n 57445K73, around 6 bucks), and a steel bar 0.5"x0.75"x4.5" Weld (or perhaps bolt) the bar to the shaft collar, and you can quickly and securely attach the proxxon to your toolpost in either configuration.
Since you can quickly unbolt the proxxon and use it for normal things (and I've found it to be a lot nicer to work with than a dremel) it's a cost effective way to have a light duty toolpost grinder.

Hope this helps,
Matt

[TXFred]

How big is the Proxxon? I'm running a 7x10 Lathe, so size and weight matter.

Frederic

[mcarvey]

The body of the proxxon is around 1.75x1.75x8" It weighs less than a pound. You should be able to fit it on a 7x10 without too many problems, although you may have to take off the tailstock.

-Matt

[TXFred]

Matt,

Thanks for the advice. I'm reading up on the Proxxon, and it really does look nice. Even better, it's one of the optional high speed spindles for my Tormach mill. I like the fact that it can do triple duty as a high speed spindle, a toolpost grinder, and a handheld grinder.

Frederic

[RotarySMP]

I also use the same proxxon IB/E grinder on my 7x12 lathe. The bearings are not great (it only has one miniature bearing in the nose with the back of the spindle relying on the motor bearings. I couldn't get a very good surface finish till I started using the thin cut off discs (like in Mcarveys post.)

Once you start getting into grinder tolerances, you get a real clear look at how crappy these 7x lathes are I got a pretty decent finish on the ER-32 collet spindle I made though.

I have a nearly finished tool post grinder I made which takes the same Proxxon collets, but haven't got around to doing the pulleys for it yet, been on a guitar playing trip rather than CNC lately.

http://www.cnczone.com/forums/vertic...pindles-4.html

[mcarvey]

I got the Proxxon primarily because I needed a precise light duty toolpost grinder, and figured that it would also be useful as a hand held tool. One of it's major advantages is the fact that that it's speed doesn't change based upon cutting load, which allows you to use it at it's lowest setting (unlike a standard Dremel) It's also much quieter, which is an added plus. It's a great little tool. Just out of curiosity, what are you doing that requires a tool post grinder?

-Matt

[mcarvey]

That was the only project in which I've used the Proxxon as a "toolpost grinder." Keep in mind that I was taking very light cuts and really only needed it to do slitting. As RotarySMP indicated, it clearly has some limitations and is by no means a replacement for a more dedicated tool post grinder (especially if you're trying to do precision bearing work). It's definitely way better than a Dremel though.

RotarySMP, your quote in the linked post was the funniest thing I've read all day. It's oh so true. "Once you play around with this stuff for a while, soon or later many of us get an unhealthy interest in making our own spindles." Haven't tried making my own yet, but can't say I haven't seriously considered it.

-Matt

[TXFred]

Just out of curiosity, what are you doing that requires a tool post grinder?

For a while I had access to a SL-20 lathe, and used it to run off a dozen Tormach tool system holder blanks. Unfortunately, the only metal I could source on short notice was 1018, so even with the lathe working happily, the surface finish was not the greatest. If I had some 4140, they would have come out looking perfect.

Because of this, I made the tools a few thou oversize so I could grind the shanks to a smooth finish.

My lathe has tapered roller bearings and a very well adjusted saddle. Between that and taking only a few tenths of material per pass, I hope to be able to get a good final finish.

Once the shanks are finished, I will put them in the tormach's spindle and use it in vertical lathe mode to finish the toolholders.

Even with the cost of the Proxxon grinder included, I should come out about $150 ahead, versus the cost of a dozen Tormach set screw tool holders.

I just wish I had made even more blanks!

Frederic

[TXFred]

After reading all of your good advice, I chose to ignore it and set up my old flex shaft tool as a toolpost grinder. The pencil's body was the exact size to fit my boring bar holder, so it was just too tempting not to try.

First I tore the pencil down, cleaned it, and did some things to try and remove slop from the bearings. I got it down to 0.005" of side play.

My test grind was to true up and face off the jaws of my 3 jaw chuck.

I couldn't grind more than 0.001" at a time, and my finishing passes were much less than that. Once I had a good surface, I took multiple passes at the same depth, using full speed on the grinder, slowest possible speed on the lathe chuck, and an extremely slow feed rate.

Results were not bad at all. It's not a professional job, but it serves well enough for this cheap little chuck.

I'm still after a Proxxon or better for a permanent solution. But this came out good enough that I am going to try grinding the shanks of one of my TTS blanks.

[mcarvey]

Hey, a success is a success even if you don't do it my way If the flex grinder fit in the holder easily there is simply no reason why you wouldn't try it. If you do end up getting a proxxon, please post feedback on how it worked for you. I haven't done a direct comparison recently.

-Matt

[jamesl]

I used an older rotozip that has a nice machined shoulder on the collet end of the machine that can be used to make a mount to fit in the tool holder. Since the rotozip has a 1/4" collet capacity it can take a much bigger cut off or grinding stone, also variable speed.