View Full Version : Problem using dovetail cutter
07-03-2007, 12:07 AM
This is my first attempt to use a dovetail cutter, and I have couple of questions.
1. I'm getting quite a bit of chattering, which leave chattering marks on the inside cut. I'm using conventional milling. The only way to get around this is to reduce the feedrate such that instead of making chips I'm making powder. Is this the nature of the cutter or is my setup (EMCO Compact 5) simply not rigid enough for this kind of operation?
2. HSS dovetail cutter was wickedly sharp but after cutting only two 2" length, it no longer has that razer sharp edge. It's still sharp, but I'm wondering if this is normal?
07-03-2007, 12:25 AM
07-03-2007, 03:45 AM
Copied from an old post last year:
I think that .002 - .005 per pass would be fine for a finishing cut. Depending on the rigidity of the machine & setup you can go a lot deeper. You need to use a slow speed and slow feed, and coolant helps.
The cut below was done in 3 passes. Material is mild steel and the cutter HSS. First and second cut about 0.100" deep then 0.010" on the finish cut. After the initial cut I dropped the table by 0.002" as these cutters can chatter when they cut on both the bottom and sides at the same time, then put it back after the finish cut for a clean-up pass. Coolant applied by hand with a squeezy bottle.
Also, don't climb mill with a dovetail cutter (except on a 0.002" finish pass maybe ) as they will *really* suck into the cut.:D
07-03-2007, 10:39 AM
I'd have possibly tried to rough it out using as solid a "woodruff" (key) cutter (preferably with "staggered" teeth) as possible or a single point fly-cutter.
Thats how I cut dovetails -- open the channel as much as possible with an endmill, and then notch out the undercut with a Woodruff cutter.
I use a single-insert carbide dovetail cutter to rough out the angle, and then take a final climb-milling cut with a HSS dovetail cutter (which leaves a much better finish than the carbide insert cutter).
By the way, there's a guy on Ebay selling American-made carbide insert dovetail cutters (with the insert) for around $30 - $40. The commercial dovetail cutters have the insert pocket cut at a 15° axial rake (just like the lead-in rake on your HSS dovetail cutter's flutes) so the insert doesn't hit the workpiece flat and hammer/chatter.
The only downside to his dovetail cutter is that is uses a rare insert: the TPGB 2.521. If you treat it well, the three cutting points will last you awhile, but finding a replacement isn't easy...
07-03-2007, 12:24 PM
Thanks for all the great ideas.
I'm a little confused about whether to climb mill or conventional mill when using dovetail cutter.
I have try both and found that climb milling produces a nicer finish, but seems to make more unpleasant noise and vibration when cutting.
07-03-2007, 12:40 PM
The loss of the razor sharp edge does not mean that the cutter is not sharp. When I was an apprentice in the tool and die business, the head of the milling department told us to always stone the razor sharp edge off with a fine india stone. He said that the thin edge was prone to flaking and by slightly flattening it the edge would hold up longer and cut better.
I knew him for many years and worked for him for several and what he told us was always very helpful.
If it was me, I would rough the dovetail with a fly cutter, as was suggested. They work good providing there is clearance.
07-04-2007, 06:36 AM
07-04-2007, 12:00 PM
Is it just a reflection in the picture, or is that second endmill threaded?
I've never seen a threaded endmill before :)
07-04-2007, 12:11 PM
Lazlo, the threaded end mill is designed to be used in a Clarkson Autoluck chuck, although you can use them quite happily in a normal collet.
The end mill screws into a special collet held in the chuck, and these won't come loose or move at all under a heavy cut, and will tighten up rather than loosen.
It's like a much better version of the weldon shank but even more secure :D
Picture of the chuck and collets here:
07-04-2007, 01:42 PM
It's like a much better version of the weldon shank but even more secure
Wow, that's neat Peter -- thanks for the pictures.
You Brits can be pretty clever at times ;)
By the way, the Clarkson collets look like normal spring collets (although if I understand correctly, you're saying they're threaded internally).
Can you use a normal (smooth) shank endmill in a Clarkson collet?
07-04-2007, 03:39 PM
No, you can't use a normal smooth shank in the Autolock chucks, you have to have the threaded end.
I don't use the autolock chuck myself, pretty much everything I do is using an ER32 or standard R8's. I never take really heavy cuts, as I don't think we need to as mere HSM's - time is usually on our side.
07-04-2007, 07:13 PM