Author Topic: milling dovetails (Read 11239 times)

Chuck in E. TN · « **on:** July 23, 2011, 03:59:50 PM »

Hey all,
I should soon receive my first dovetail cutter. As I have never used one before, can someone with experience lead me through cutting a dovetail, please?
I am building Howard Hall’s Deluxe Grinding Table. I have cut the channel in the parts with the internal dovetail and machined to size the parts with the dovetail on the outside. All that remains is to cut the dovetails themselves.
I have an X2 mill. Do I use cutting oil?

Chuck in E. TN

dickda1 · « **Reply #1 on:** July 23, 2011, 04:05:54 PM »

Take a look down the page on this topic. Bogs has some good advice for cutting a dovetail.

http://madmodder.net/index.php?topic=2323.0

-Dick

DaveH · « **Reply #2 on:** July 23, 2011, 04:57:50 PM »

Hi Chuck,

I wondered where you had gone

Some more here.

http://madmodder.net/index.php?topic=5664.msg60016#msg60016

DaveH

Chuck in E. TN · « **Reply #3 on:** July 24, 2011, 08:41:21 AM »

Here’s pictures of what I’m cutting dovetails in.
I have already milled the waste away where I could:

Chuck in E. TN

Chuck in E. TN · « **Reply #4 on:** July 24, 2011, 09:43:18 AM »

The block at the bottom of the second pic, with the small slot in the middle, will be one of the male dovetails. Should I cut male first, as I'm creating a entire new dovetail, and not making a part to fit an existing one?
I had intended to make a indexable dovetail cutter for roughing out, but haven't decided on what insert to use. I checked the local Fastenal and they didn't have any in stock to try.
I ordered a HHS dovetail cutter from CTC Tools, but it hasn't arrived yet.

Chuck in E. TN

Chuck in E. TN · « **Reply #5 on:** July 27, 2011, 09:58:49 AM »

Well, I ran a test on the indexable dovetail cutter. Bear in mind, it's the first time I've used an indexable tool of any kind. I skipped the aluminum and went with mild steel. I started cutting a male(?) dovetail. Speed 750 RPM, cutter dia is 1 1/4 in. I baby stepped the cuts, .005 doc, and hand cranking (no power feed), and applying oil via a pump oil can, like Dorothy used on the Tin Man.
It sounded like a jackhamer, thump-thump-thump. At one point the chips were smoking. I turned the rpm up to 950 and the chips smoked a little more. Dialed in too big a cut one time and stopped the spindle (belt drive, thank goodness).
I did not lay out a specific starting point, just chucked up a 1" square scrap and attacked it from the side, about 1/4" down from the upper surface, and ran conventional cuts untill the cut wasabout 1/8" deep. If I had set up the cut as per the ones I'm going to make, the result would have been bigger and probably easier to see in my photos, Test 1 thru Test 4, here:
http://s571.photobucket.com/albums/ss157/chucketn/Machining/dovetail%20cutter/
If you look close, the insert is chipped resulting in a pronounced radius in the dovetail. That probably happened when I jammed the cutter.
Any comments? Anyone know of an Excel based feed and speed calculator, standalone?

Chuck in E. TN

John Rudd · « **Reply #6 on:** July 27, 2011, 10:13:53 AM »

Quote from: Chuck in E. TN on July 27, 2011, 09:58:49 AM

Well, I ran a test on the indexable dovetail cutter.
If you look close, the insert is chipped resulting in a pronounced radius in the dovetail. Any comments?
Chuck in E. TN

I think your first mistake is in using an indexable cutter...Maybe others have a different opinion ?

Carbide doesnt stand up to shockloading as it is brittle.

Good for continuous cuts but not interrupted...Better off with a hss tool.

DaveH · « **Reply #7 on:** July 27, 2011, 10:34:33 AM »

Chuck,

You don't need a stand alone speed feed calculator. Moreover there isn't one.

I think you have cracked it -950 rpm suits you, your feed, your cutter and your machine.

Don't worry to much about the (horrible) thump thump thump - it is just the action and noise of a single insert. I know it is a little off putting - but at least you now understand what your machine is having to put up with. (My machine is exactly the same).

The chips will come off hot and fast.

Cutting a dove tail is a difficult proceedure. Seems to me you have done it.

A smaller cut, with a faster feed may be benifical. Normally better than a large cut with a slow feed.

All this roughing out will save your HSS dove tail cutter no end.

Now when you come to use the HSS dove tail cutter reduce you speed to 500rpm. Just see how it goes first.
Keep the cuts small .005 see how it goes, with the feed test faster - slower.

I t is just a slow process Chuck - trying to not break the HSS dove tail cutter.

If all looks good increase the speed and feed if you want to, but just be carefull with the depth of cut.

The HSS dove tail cutter makes a nice noise - brrrm.....brrrm.....brrrm much more reasurring

DaveH

DaveH · « **Reply #8 on:** July 27, 2011, 10:38:58 AM »

Chuck,
John is absolutely correct in what he says.

John,
Chuck is cutting his first dove tails he is just using the insert cutter he made to do the roughing first, he'll finish with the HSS one.

DaveH

Chuck in E. TN · « **Reply #9 on:** July 27, 2011, 10:59:43 AM »

I guess next step is to go set up to make the real cut in the other side of the test piece. That is, make the dovetail to dimention.
So, my speed is good, doc .005? How do I prevent the chipping of the insert? More cutting oil?
I have a Shumate DRO on the mill, but the y-indication seems to jump around when cutting in this setup. I learned to lock the non changing axis, in this case the y and z, when milling. I also have built a tach sensor so I can set RPM.
I have already realized I can't use this tool to rough the femail dovetails in the actual project, it's too big in dia. (1 1/4"), so I will have to make a smaller one! Yay, more toolmaking!
And, thanks for all the input, support.

Chuck in E. TN

DaveH · « **Reply #10 on:** July 27, 2011, 11:49:34 AM »

Chuck,

Like John said, carbide is brittle, and does not like interupted cuts, try to be careful when starting the cut.(Enter the material slow)
And yes lock all non moving slides

Try it without the oil - I know it goes against your instinct, but the carbide doesn't mind!

The HSS cutter may benefit from some cutting fluid. Put some on the machined dove tail - run the cutter thro' clean the cutter and the work piece, of chips. Repeat the process.

Yep sure is slow this, but at the end of this we are going to have an expert dove tail cutter.

And a still usable HSS dove tail cutter

DaveH

AdeV · « **Reply #11 on:** July 27, 2011, 01:27:26 PM »

FWIW, my experience of using a HSS dovetail cutter is this:

1) Run it SLOWLY. 300rpm is plenty. Remember, it's a multi-flute cutter, so you still get plenty of cutting effort, even at reduced rpms. Run it too fast, especially in steel, and you'll just blunt it.

2) You can take a couple of quite big bites (0.1") as your initial cut, but as the length of cut gets longer along the blades, each bite gets smaller and smaller. My last-but-one increase is usually 0.010"; the final increase is much smaller & is just for finishing.

3) Assuming you're testing your dovetails for fit, and want only tiny amounts of slop; don't forget to slightly round the top edges with a file, to encourage the dovetails to mesh. Sharp pointy edges will not forgive any misalignment when you fit, and you'll end up over-cutting & will have a sloppy dovetail.

4) The more cutting fluid the better. I've now poured enough neat oil into my sump that I can flood-cool with it, so I do. It makes a real difference to a dovetail cutter (the flutes tend to clog up)

Chuck in E. TN · « **Reply #12 on:** July 27, 2011, 03:08:39 PM »

A member on another forum pointed out a mistake in my cutter. I had milled the pocket to the centerline of the cutter, thus the cutting edge of the insert was above the centerline by it's thickness. I still had the setup for milling the pocket on the mill table, so I fixed that. I then cut a 1/2 dovetail to plan specs for the HH Grinding table. It looks good enough that I may not bother to touch it up with the HHS cutter when it arrives...
Pics of the cutter rework and the second dovetail here:

http://s571.photobucket.com/albums/ss157/chucketn/Machining/dovetail%20cutter/

I did use the same piece of scrap for the second cut. Second cut is bigger than the first. Now I need to find a smaller insert and make another smaller cutter!

Chuck in E. TN

DaveH · « **Reply #13 on:** July 27, 2011, 03:45:24 PM »

Chuck,

Let me just say if you don't need to use the HSS dove tail cutter, thats one fine piece of milling, with a home made insert cutter.

DaveH

Chuck in E. TN · « **Reply #14 on:** July 27, 2011, 04:10:03 PM »

Oh, this economy sux! I really cannot see paying $20 for 10 inserts, and $11 UPS Ground shipping. Anyone have a good source for TCMT inserts, 3/8"IC, that won't require a second income for shipping?
I can see paying $2-$3 per insert, but half again in shipping?

Anyone that buys inserts in large quantities want to sell me a couple + postage? I want to make another Dovetail cutter 3/4" in dia.

Chuck in E. TN

Country Bubba · « **Reply #15 on:** July 27, 2011, 04:47:10 PM »

Chuck,
I get a lot of my stuff from Enco and make my orders up to the min. for free shipping! As you well know, it doesn't take a lot to make up a $50 order.

Chuck in E. TN · « **Reply #16 on:** July 27, 2011, 05:23:03 PM »

Can anyone translate the size of this:
TCMT 1.8(1.5)2-UM 4025 SANDVIK
I understand the TCMT part, what would be the length of one side of the triangle?

Chuck in E. TN

DaveH · « **Reply #17 on:** July 27, 2011, 05:47:15 PM »

Chuck,

In mm's the length of the cutting edge is 9mm
The thickness is 2.5mm
And the radius (of the points) is .8mm

DaveH

Edit Thickness 2.5mm not 2mm

Chuck in E. TN · « **Reply #18 on:** July 27, 2011, 06:53:08 PM »

Thanks Dave, that will work for a 3/4" dovetail cutter.

Chuck in E. TN

DaveH · « **Reply #19 on:** July 27, 2011, 08:45:37 PM »

Chuck,

Apologies mate I told you wrong.

It is 2.5mm thick not 2mm thick Sorry chuck

DaveH

Chuck in E. TN · « **Reply #20 on:** July 28, 2011, 06:57:20 AM »

Dave, the radius of the points, is that the radius of the IC, or the radius of a circle encompasing the points?

Chuck in E. TN

AdeV · « **Reply #21 on:** July 28, 2011, 07:35:09 AM »

Quote from: Chuck in E. TN on July 28, 2011, 06:57:20 AM

Dave, the radius of the points, is that the radius of the IC, or the radius of a circle encompasing the points?

Chuck,

This page should answer your every question: http://www.grainger.com/Grainger/SANDVIK-COROMANT-Carbide-Turning-Insert-5JWY0

DaveH · « **Reply #22 on:** July 28, 2011, 07:40:02 AM »

Chuck,

The radius .8mm is the radii of the 3 points of the triangle.

DaveH

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Author Topic: milling dovetails (Read 11239 times)