Reaming A Collet?

F

fatphatboy88

Registered
Registered
Joined
Mar 31, 2014
Messages
14
On our CNC routers at work, we have some collets that I would like to ream out. We do not have gang drills on our machines so we just use a normal tool holder with a Shars drill chuck attached to it. The problem is that with the long drill bits and the added length from the drill chuck itself, we are maxed out on positive Z-axis travel sometimes. We have to use jobber length bits instead of screw machine length for the depths we are drilling. Our HSK-63F tool holders use SYOZ-25 collets.

I am hoping I can ream out a spare 1/4" collet to hold a 17/64 drill bit and a spare 5/16" collet to hold a 21/64. How would I go about getting the correct tension on the collet in order to ream out the center?

We have a small Grizzly 9" lathe that I could put them in to ream. I also have a couple of old tool holders that I could put the collets into ream. Just dont really see how to get the correct tension on them except for maybe wedging some tiny shims in the slots before tightening down the collet nut.

I have no clue what the collets are made out of either. I am assuming its made out of some type of stainless since I have never seen a spec of rust on any of them, including some old used ones we got for free.
 
I think you are going to find that those collets or almost any collets for that matter are going to be too hard to machine. Maybe a carbide reamer would do it. You would be better to just buy new collets the correct size.

But the way to pre-tension the collet is to put the correct shims in the slots to keep the collet from collapsing while machining it in the holder.

You would be better off to turn down the drill bit shank to the collet size, at least they are easily machinable.
.
.
 
Last edited:
I don't know about collets for routers but collets commonly used in metalworking are hardened steel. Additionally, because a collet is slit to allow it expand and contract, you would not be able to stabilize it to permit you to ream it. There are machinable collets but they are made so pins can be inserted in the slits to stabilize the collet while machining. For hardened steel collets, you would have to use a grinding procedure. EDM (electrical discharge machining) would also work. A carbon electrode of appropriate diameter would be used to "burn" a new hole. Because there is no cutting pressure involved, you would not need to stabilize the collet.

Thinking outside the box, instead of enlarging the collet, why don't you turn down the shank of the drill bit to fit your existing collets. High speed steel drill bits are machinable and this is a very simple and quick procedure. When i have needed extra long drill bits in the past, I have turned down the shank of the drill bit with a carbide bit and drilled a socket in the end of a long rod the same diameter as the drill. I then brazed or super glued the drill bit to fix it in place.
 
JimDawson said:
I think you are going to find that those collets or almost any collets for that matter are going to be too hard to machine. Maybe a carbide reamer would do it. You would be better to just buy new collets the correct size.

But the way to pre-tension the collet is to put the correct shims in the slots to keep the collet from collapsing while machining it in the holder.

You would be better off to turn down the drill bit shank to the collet size, at least they are easily machinable.
.
.
Click to expand...
Jim, notice of your post came through just as I hit the "Post Reply" button. I like the idea of the shims though. I had forgotten about that one.
Bob
 
Great minds think alike I guess :grin:
 
We have turned down the shank before, but the boss sees that as a waste of time and money since we change them fairly often. Too much work for a $2-4 drill bit. That's why we got the drill chucks to make changing them easy.

The problem with SYOZ-25 collets is that they start at 1/8" and move up in increments of 1/16". The collet manufacturers have already told me a big fat NO on making a couple of custom sized collets.
 
You could always see if the boss would be willing to spring for a HSK-63F ER collet holder instead. I think an ER-16 set should cover your sizes fairly well.
 
I've never used that type of collet & don't have much knowladge on the matter so take this as more of a question then a suggestion. I can fit 1/34 up or down of the correct shank size in my R8 collets. My center finder is a 10mm so I have to jump way up to 7/16 to hold it. It has seemed to work for me so far. I may be doing something to damage something else tho. I have been knowen to do stupid things before. I usually lean after breaking something.
 
Shims and internal grinding. Would need a tool post grinder to do it on the lathe. With ID grinding adapter.
 
The only other thing I can think of is to make a split sleeve to adapt the drill bit to the collet. Given that the spindle turns about 18,000 RPM you'll want it pretty accurate.
 
You must log in or register to reply here.
Back
Top