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Cutting dovetails, how hard can it be...

 
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  #15  
Old 03-25-2012, 11:31 AM
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Re: Cutting dovetails, how hard can it be...

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Originally Posted by Jinx-) View Post
I think I dislike working on the Bridgeport mill, even when it does have 30+ year old cnc controller for XY axis, basically it took 8 hours today to contour and cut dovetails and they have -.002 plus nothing tolerance, well its going to be aloris piston tool post when its done, it should resemble something like this http://www.contractmachining.us/fors...dwk12_4968.jpg
years back I was making some measurments on a machine in one of the other plants, and saw this big tool block in the scrap tub. Right with it were a dozen or so tool holders. The guys said the tool block was junk and couldn't find another one. I'd only worked with the the Alorus tool blocks. and this one was different. But it was also bigger, and I had this one LeBlond hand lathe that would swing about 24". So here I come back with all these holders and the non working tool block. Had it working in twenty minutes. Took it down to the guy on that big lathe, and he wanted to try it right away as he was using one much smaller. Mo loved that block, and the holders (can't remember the brand name, but started with a D). I gave one of the holders to a tool engineer that I often bought stuff thru, and ask him to find a supplier. Next day he says he has two, and what do I need. Mo makes of a list of stuff, and we never looked back. I made a couple tool holders for an Alorus years back, and cut them out on a wire edm. Think I used 4150
gary
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  #16  
Old 03-25-2012, 11:38 AM
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Re: Cutting dovetails, how hard can it be...

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Originally Posted by Bullet bumper View Post
You seem to be cutting the base as well as the angle . Dovetail cutters don't like cutting on both faces at the same time The shoulder for the dovetail can be cut with a normal end mill but about .015 too shallow. Then use the dovetail cutter so it is only cutting on the side and move in while not cutting anything on the base of the cut . Use conventional milling only and very light cuts. Don't heat up 1020 as it will harden.
When the dovetail is getting near to specks drop it down and mill out the .015 on the base them move in and mill the inner edge to specs.
From the chips on the edges of the cutter you are just going in too deep at a time . They are very slow cutting and you have to be patient .
that's pretty much what I ment by relieving the base of the dove tail, so that at the very most you are only cutting about .005". The real problem is the machine itself. The spindle bearing pack is not all that strong. Had he been using a knee mill it'd been a piece of cake. Relieving the sharp corner with a saw cutter will also help out a bunch. Then you are also dealing with 1020 CRS. A very gummy like steel. 8620 would have cut a lot better. But in the end if you want an accurate dovetail, you can either wire it out or single point it on a shaper.
gary
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  #17  
Old 03-25-2012, 12:23 PM
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Re: Cutting dovetails, how hard can it be...

Gary, after doing some research it seemed that piston style toolpost would be less difficult to reproduce, I already made everything for it for the exception of dovetail block....



I used solidworks to design this piece and block itself is the only complicated part I still have to work on.

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  #18  
Old 03-25-2012, 07:47 PM
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Re: Cutting dovetails, how hard can it be...

it's called rigidity, or in your case, a lack thereof.
Tighten that Bridgeport up.
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  #19  
Old 03-25-2012, 11:01 PM
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Re: Cutting dovetails, how hard can it be...

It's an old machine and moving table just .0001 makes test indicator jump .0005 while its placed on gauge block, that's when no stress applied, imagine running dovetail cutter or slot cutter... When I was cutting my first dovetail on it, I felt like table was jumping .05 or more, but that was on crossfeed. So yes its an old machine and good tuneup would probably help a lot.
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  #20  
Old 03-26-2012, 07:33 AM
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Re: Cutting dovetails, how hard can it be...

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Originally Posted by WapitiBob View Post
it's called rigidity, or in your case, a lack thereof.
Tighten that Bridgeport up.
Yep! Thats where 'chatter' come from. Poor set-up, improper work holding, improper tool holding (your worn gibs fall under improper work holding). Gary, got a 16" John Steptoe settin' here. There be just a few of us that visit these forums that could still make a tool and set-up and make it produce. Haven't used it in a couple of years, now. But when you need it, you really need it! There are some jobs that are still done best with a shaper.
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  #21  
Old 03-26-2012, 08:03 AM
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Re: Cutting dovetails, how hard can it be...

Quote:
Originally Posted by Trickymissfit View Post
years back I was making some measurments on a machine in one of the other plants, and saw this big tool block in the scrap tub. Right with it were a dozen or so tool holders. The guys said the tool block was junk and couldn't find another one. I'd only worked with the the Alorus tool blocks. and this one was different. But it was also bigger, and I had this one LeBlond hand lathe that would swing about 24". So here I come back with all these holders and the non working tool block. Had it working in twenty minutes. Took it down to the guy on that big lathe, and he wanted to try it right away as he was using one much smaller. Mo loved that block, and the holders (can't remember the brand name, but started with a D). I gave one of the holders to a tool engineer that I often bought stuff thru, and ask him to find a supplier. Next day he says he has two, and what do I need. Mo makes of a list of stuff, and we never looked back. I made a couple tool holders for an Alorus years back, and cut them out on a wire edm. Think I used 4150
gary
Lets see, 8 hours and chatter from worn (probably loose gibs and worn ball screws), would be more expeditious to buy an Aloris tool post, preferrably wedge lock over piston because the repeatability of a wedge lock is far superior to a piston in all aspects.

Your 'D' toolholders are Dorian Tool. Everything is interchangeable wedge or piston in toolholders. I run Aloris wedge locks exclusively with generic (Phase 3 toolholders). The accuracy and repeatability is in the block itself, not in the toolholder.

We too have a shaper. It's the only machine for cutting dovetails and negative relief on die's. Other than that, it's a large paperweight.

Of course Gary, you were using someone else's machinery, time and electricity. That's why shops loose money. You can make anything but you need to look at the end game and the cost. Business operates for a profit, not a hobby.
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