Making a 355 Collet for Deckel SO tool and cutter grinder

[Winegrower]

I got this Kunming clone of a Deckel SO grinder, and it's very well done. It's pure Chinese, People Republic of China stuff. I notice that compared to some clones, this model has the drive belt and motor completely enclosed in the unit, and the belt is at the opposite end of the spindle from the wheel. That makes it pretty compact and keeps grit far away from the belt.

I watched a bunch of good YouTube videos and figured out how to do things like 4 facet grinds on drill bits, and how to make say, a 0.030 radius end on a carbide tool. The precision and flexibility of control is really impressive (and fun).

But the set of 7 collets that it comes with, and seem to be the standard equipment set for these tools are all for round bits. I would like to make lathe tools with a lot of 5/16" square HSS blanks I have. So I looked for square collets...available, but real Deckel collets seem to be in the $350 each region, though I did find some for maybe $35 or so. It's a hobby, so taking a day or so to make one seemed feasible.

I found a drawing with some of the dimensions, and got the rest from direct measurements on my set. The most interesting feature is that the thread is not a typical V thread, but is a "buttress" thread, designed for applications where the force is predominately from one direction. And of course, it's metric. I measured it to be 20mm with a 2mm pitch.

Machinery's handbook shows buttress threads as having a 45 degree included angle instead of the 60 degree for a V thread. And one of the faces of the threadform is basically perpendicular to the axis of the shank. I thought about grinding a lathe tool for this but I have a vertical insert holder, with triangular vertical inserts, so in just a few seconds I ground off 15 degrees or so from one side of one of the insert tips. Then I set the tool post so that the unground face was normal to the spindle axis. This worked basically perfectly, so standard procedure from now on will be to first consider stock inserts, if not that, grind some insert to fit, if not that then make an HSS tool.

In any event, it was a successful project. Steps included setting the compound to 17.5 degrees and verifying against an existing collet, drilling and broaching with a 5/16" square broach, changing the gears around for 2mm pitch (for the first time, brought up some new issues and subgoals), slitting the collet at the four corners of the broached hole, and turning the metric buttress thread (first time for metric threads, too).

This square collet with the grinder is going to make some operations very easy, like O ring grooves, trepanning, etc,

 

[GeneT45]

If you can convert it to 5C, that will be the biggest upgrade ever. Every type of collet is available in 5C, including non-round shapes. Your best alternative* is to make a lathe tool grinding attachment, which replaces the collet holder. Some of the other import units come with such a beast.

GsT

* Actually, your best alternative is to learn to grind lathe tools "freehand", or at least with very little support. My Deckel clone came with a lathe tool grinding attachment, but I've never used it because once you've learned to grind lathe tools there's really no need for a fancy machine. Someday I may use it for something dimensionally specific, but for general turning tools you're much better off investing the 90 minutes that it takes to learn to grind general purpose lathe tools.

 

[pontiac428]

The Kunming castings are barely discernable from the Sheckel or the eBay U3 clone. Spend the $90 for a 5C workhead. 5C goes up to what, 1-1/8" or so? Huge gain over the smallbore Deckel collets.

I have not found square collets to be useful without knocking out the indexing pin in order to allow base clocking. I still prefer the lathe bit workhead.

I don't see any blood anywhere, so I imagine you're just getting started.

 

[Winegrower]

Spend the $90 for a 5C workhead.

Really? They would fit? Great idea if it's possible. Seems like the center height would change and mess things up. I'm not sure how to evaluate this option. Standby...

I have not found square collets to be useful without knocking out the indexing pin

I don't follow. I aligned the pin/keyway for zero on the dial. The holder can free wheel to any position, lock every 15 degrees, or stop at 0 and 180. I don't see the pin limiting this? Explain please?

About blood. So far, you're correct.

 

[Winegrower]

Humm...these U2 collets seem to have the same spec as Deckel collets, and are not much different in price than 5C. I don't see specs on the thread, if it's buttress, then if you can get square collets I'm good.

Seems like square collets will be much better than you guys predict. I'm off to find out.

 

[pontiac428]

Yes, the workhead for the U3 is a direct fit on the dovetails, or you can swap the whole unit on the way rail. Worst case scenario would involve making a rectangular gib to make up any dimensional differences arising from the black box of manufacturers behind the bamboo curtain.

Speaking from experience, I prefer the ubiquitous 5C collets, it's an open and shut decision as far as I am concerned. The reason the Chinese are making Deckel collets today is because of demand- there are a lot of Deckels out there missing collets. It's not their tiny max size range that makes them popular, I'll tell you that!

The square collets I bought are from Shars (and are 5C, of course). I put one in and got it clocked to zero on the dial, then I punch marked the pin's position on the collet reducer body or work spindle, whatever you want to call it. Then I checked the other square collets... yeah, no dice, they're clocked different. Should have bought Hardinge, d'oh. To this day I have not ground a lathe tool in a square collet. I use the lathe bit workhead (available for the U3 on eBay for $65 or so) exclusively.

As far as changing center height, that's not really an issue within reason. It's a swing arm that moves a tool in plane with the grinding wheel, that relationship is not affected by center height. Truth is, you change the swing height every time you change the length of the tool you are grinding. You will get a feel for it after some use.

The art form here comes with grinding features that are outside of the machine's work envelope. That separates the men from the boys. Your ability to think creatively and accomplish your task is what makes these little grinders shine. If you paint within the lines, it's a D-bit grinder. If you can work outside the box, it's so much more.

 

[Winegrower]

I'm finding the square collet is pretty useful in the cutter-grinder. It was a snap to cut a trepanning tool, using SolidWorks to plan the relief angles that would cover the range of diameters I wanted. Yes, you Bulls of the Woods would just walk over and hand grind a tool, maybe hone it on your teeth, but this square collet and a 5/16 HSS blank worked well for me.

Well, I bought a U3 5C head anyway...and what's worse, I made an adapter so I can use my accu-flex collets to hold drill bits for four facet grinds, and any other random diameter tools that need grinding. These collets may span the range better than my 5C set. See photos. In the process, I thought I would re-use the nut that comes with the Kwik Switch collet holder. It has a more or less square thread, so I had a vertical triangle threading insert and hand held it to the diamond wheel on the cutter grinder and in about 10 seconds had a square thread tool. It worked way better than I expected.

 

[petertha]

More food for thought. I happened upon this this video. At 1:47 is shows what looks to be a shop made collet to fit his (presumably U-collet) work head but with what looks to be an ER-16? nose. Its obviously bored out to accommodate stock/shank length like the stock collet. I posted a question to that effect but he hasn't replied yet. I can see certain operations where ER would lend itself to grip wide range of oddball stock diameter 7 with fewer collets. But might also get in the way in certain operations in close proximity to the wheel.