Cutting dovetails, how hard can it be...

[Trickymissfit]

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/forsale/fixed/oct08/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

 

[Trickymissfit]

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

 

[Jinx-)]

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.

 

[WapitiBob]

it's called rigidity, or in your case, a lack thereof.
Tighten that Bridgeport up.

 

[Jinx-)]

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.

 

[shortgrass]

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.

 

[SidecarFlip]

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.

 

[Trickymissfit]

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.

I would do two very small changes in your design. First use a Morten nut instead of a regular nut, and then get the one with the male radius onthe bottom. Then secondly use the corresponding washer with the same female radius. I went with these years ago and found that the worked a little better in allowing the dovetails to align themselves easier (I had one every once in awhile freeze up on the block [Alorus]). You already have the block done, and all you need is the hard nut and washer. Never tried to make the center post, and I congratulate you on your work! Your building the small one, we used the next size bigger most of the time, except on the Hardinghs and my Monarch EE. If you can lay your hands on the threading tool holder they sell, buy it! It looks like they either used Rex 95 or Vasco Supreme for the cutting device, and it really cuts nice threads. (highspeed steel always cuts a better thread than carbide anyway). One last thing about those blocks. The stud that goes thru the block, and holds everything in place gets beat up pretty bad if in constant use. (the Morten Nut really helps it last longer). Make the stud out of pretreat 4150 with a removable tee nut on the bottom ( some are real oddballs). Then have the stud nitrided. But leave the tee nut soft as you can (I always used 8620), as you want that part to go first. Also easier on the cast iron slot in the compound on the lathe. I used to make eight or ten studs at a time, and had several nuts for each compound.
gary

 

[Trickymissfit]

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.

Best to cut the dovetail by moving the saddle, rather than the table. Lock the table down. You cannot really tighten up a Bridgeport table a lot due to it's constant flexing from over hang and wear. Their table design is their weak point. Had you been using an old K&T knee mill it would not have had one tenth the vibration from the cutter. THe next problem with the Bridgeport is the flexing of the spindle under hard loads. Most guys think it's in the cutter, but it really goes back to the weak spindle design. A Tree Mill was a much better spindle design even though I hated working on them
gary

 

[WapitiBob]

I prefer Mori NV5000 or Makino A51

 

[Trickymissfit]

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.

Honestly, the John Steptoe is new to me! I'm locked in on the idea that the best way to cut a good dovetail is with a single point tool and with a shaper or a slotter. But a wire will also do a very nice job on them. The hardest part in cutting multiple dovetails is getting both of the parallel. Every time I got the gauge pins out to measure them I always had the hair stand up on the back of my neck! (yes I did get a bad one every once in awhile) The first machine I ever ran when I was a kid in the tool room was a shaper, and learned to do all sorts of things with it that would have been a bear on a mill. Then I moved about forty feet over to a couple planers, and they looked odd at first, but boy could you do some nice work with one. Once you got the parts setup right (I had to learn from old Germans that had no sense of humor), it was simply stunning what you could do.

The single hardest parts I ever cut on a shaper were triggers! Very similar to what goes in a rifle, but three times bigger
gary

 

[Trickymissfit]

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.

you are right about costs, but when building machinery and fitting all those pieces together things are a little different. Most dovetails had to be scraped in to a male master, and then rescraped to fit the other part. A milling machine will drive you nuts when you have to master all those piece together. You don't get that from a single point machine. Grinding something that will them be scraped in is even worse.

I personally liked to cut most dovetails 6" and shorter in a wire edm if possible. A good CNC machine center would really cut those dovetails nicely (also fast). Still you'd be amazed at how fast those dove tails can be cut with a G&E shaper once you learn the game. The tool holders from Alorus look like they were either single pointed or else broached (probably broached) in one pass. It would take abbout 90 secounds to cut the dovetail in a tool holder with a broach
gary

 

[Trickymissfit]

I prefer Mori NV5000 or Makino A51

we bought 16 of those Mori Seikis, and they are junk right off the loading dock. Then boght 16 Makinos, and they ran a lot better, but were distant second class to a G&L MM2300 in work out put and down time. Even an old K&T MM800 made those guys look like third rate stuff. My favorite machine centers is still the old Devlieg J series for accuracey and output
gary

 

[shortgrass]

Honestly, the John Steptoe is new to me! I'm locked in on the idea that the best way to cut a good dovetail is with a single point tool and with a shaper or a slotter. But a wire will also do a very nice job on them. The hardest part in cutting multiple dovetails is getting both of the parallel. Every time I got the gauge pins out to measure them I always had the hair stand up on the back of my neck! (yes I did get a bad one every once in awhile) The first machine I ever ran when I was a kid in the tool room was a shaper, and learned to do all sorts of things with it that would have been a bear on a mill. Then I moved about forty feet over to a couple planers, and they looked odd at first, but boy could you do some nice work with one. Once you got the parts setup right (I had to learn from old Germans that had no sense of humor), it was simply stunning what you could do.

The single hardest parts I ever cut on a shaper were triggers! Very similar to what goes in a rifle, but three times bigger
gary

The steptoe is a shaper that uses a single point HS tool. Mine is old enough it is driven by 2" leather belt. Built by Western Machine Tool Works, Holland, MI.