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Making a dovetail fixture for the 5 axis...make it square or rectangular?

implmex

Diamond
Joined
Jun 23, 2002
Location
Vancouver BC Canada
Good morning All 5 Axis Wizards:
I'm building a dovetail block for a client to fit on a Haas TRT 100.
The load capacity of these tables is pretty small so I grabbed a chunk of scrap Ti6Al4V titanium and cut it out of that to save weight.
Here's what I originally planned:
Dove fixture 1.JPG
So the dovetail end is planned to be square...equal access from all sides.
As you can see, I have 1.6" of dovetail length.

The dove itself will be wired with a coarse finish...about like a medium sandblast, so it'll be pretty grippy.
It's 1.0" wide, 0.100" deep and is relieved in the corners.
The clamp screw is 1/4:20.
The whole fixture is 1.300" tall.

The machine is a DT-2 the spindle is ISO 30, so cutters typically under 1/2" and no hogging.
This is all Alpha prototyping...the cost is in the fuckaround factor, not how quickly I can peel metal from the block.

I have it up on the wire and I've rough cut the first side.
Here's how it looks:
dscn5736.jpg
So the question is:
Is it in my interest to leave the dovetail as long as possible?
I can gain another 1/8" if I just catch the corners of the mounting counterbores.
I can gain almost double the length if I ignore the ugly holes.
The body is 3" diameter.

This thing will potentially run the largest blocks of aluminum the TRT100 can swing for 3+2 machining which is a 5" cube.
So do I cut it per the original plan?
Do I cut it to just clean up the bolt holes?
Do I leave it as is?

What say ye...all of you with 5 axis experience.
This thing will most likely get used for such a big block maybe once or twice in its lifespan...a more typical stock size is 1" x 1" x 2" long.
Do I go for the best access, or do I go for the best clamping security?

BTW, I do have other options for clamping smaller stock...a modified Sherline 4 jaw chuck, and an ER 20 collet chuck that's been modified for dead length stops and for home made aluminum emergency collets.
I have another fixture on the go too, for clamping 3" diameter plates of any thickness, so they can be run side 1 and side 2 as if the TRT 100 were a 4th axis, to eliminate fucking around with soft jaws all the time.
That's a whole 'nother project...I'll write that one up in another thread.
I'm also going to recommend they buy one of those little 5 axis vises mhajicek recently showed in another thread.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Last edited:
It's been forever since I've worked with titanium, isn't it malleable?
I'd want something that wouldn't warp from tightening repeatedly.
 
Clearance is everything. Chop the sides.

For the rare big blocks, just go slow.

How exactly is this fixture supposed to work? Are you planning to cut a slit in the middle so it acts like a pinch block?
 
Hi Mtndew:
Commercially Pure titanium (grade 2) is fairly soft, but Ti6Al4V (grade 5) is fairly hard and very springy.
In fact, I've used it to make corrosion resistant high temperature springs very successfully
It's about like 17-4 PH H1025...so maybe 35 Rockwell C.

For this occasional use, almost exclusively on 6061 aluminum, it should wear quite well, and it's not gonna distort.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Hi Orange Vise:
Yep, you got it...if you look closely at the model you can see the slit.
Here's another view:
Dove 2.JPG
One of the incidental benefits of having a wire EDM...weird stuff like this goofy slot is no hardship to make at all.
Doing it like this makes the stationary side stable so this contraption is super repeatable which is occasionally valuable.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
One thing that is for sure, whether short or long, it will be wrong.

Why not make a few out of aluminum so you have various sizes, on their 5 axis mill? Will these fixtures see enough use that they need to be hard? I would think aluminum would be good for several thousand cycles.
 
Hi DavidScott:
Yeah I could, but I just happened to have that nice chunk of titanium bar kicking around, so I grabbed it and put it to use.
But you make an excellent point...I've got a ton of tooling I built for myself over the years that just never did make it into the heat treat furnace, and I've put a billion miles on it since I made it.

But it's just me, noodling along so I know to take care.
Put it in a regular shop environment and it won't last a month...if the guys are "Brisk" enough, even the hardened tools won't lat a month.
You should see what those bastards did to my matched A-2 63+Rockewll C grinding vises...I foolishly lent them to a co-worker and they came back so fucked up I had to re-grind them.
I don't lend out tools anymore.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Hi again plastikdreams:
Gotcha...thanks.

So I am building out this customer's shop.
They want to be able to mount stock to their rotary and they have nothing with which to do it.
So I need to buy if I can and make something if I cannot.
Turns out the available offerings are all designed for much bigger platters than the TRT 100 has, so I'm having a hard time finding something that will fit and not be a major compromise in one way or another.

Starting out by bolting up a 3R wire EDM rail sadly doesn't solve my fundamental problem...I'd still have to custom build everything that clamps onto the rail.
I don't need what the rail can offer, mostly I need to be able to resist milling forces, and I need to be able to get unrestricted access to 5 sides of my part.
Bolting my custom gadgets directly to the TRT platter ensure they're mounted rigidly, and if a guy has to remove 6 bolts to dismount a gadget and torque up another 6 bolts to mount a new gadget, that's no hardship.

Somewhere in there, is a minor business opportunity for someone, because I cannot believe other TRT 70 and TRT 100 owners haven't confronted this exact same problem.
I'm way past the age where I could contemplate getting something like this up and moving, but somebody could perhaps do a decent small trade in something like this.
Sad reality is you might get 50 sales a year in the first 5 years and then everybody who wants one already has one.
Every serious manufacturer like say a medical jobber, is not going to pin his production hopes on a TRT 100...they want something with way better accuracy specs.
The TRT 100 is only accurate to 45 arc seconds, and that's on a good day!

I'd be curious to see a business case...none of this stuff is hard to build, but it's a real PITA compared to just going to the fixture store and dropping a bit of coin.

Orange Vise...do you have thoughts on this?

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Hi SteveEX30:
This is for mounting workpieces just like you'd mount stock in a 5 axis dovetail vise.
You just have to take care to make the dovetails on your stock the correct size because the clamping range is so small.

I'm hoping the super coarse wire EDM texture in the dovetail will give a good grip and allow me to avoid a stop...if it's not enough I'll add a positive stop.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Hi again plastikdreams:
Gotcha...thanks.

So I am building out this customer's shop.
They want to be able to mount stock to their rotary and they have nothing with which to do it.
So I need to buy if I can and make something if I cannot.
Turns out the available offerings are all designed for much bigger platters than the TRT 100 has, so I'm having a hard time finding something that will fit and not be a major compromise in one way or another.

Starting out by bolting up a 3R wire EDM rail sadly doesn't solve my fundamental problem...I'd still have to custom build everything that clamps onto the rail.
I don't need what the rail can offer, mostly I need to be able to resist milling forces, and I need to be able to get unrestricted access to 5 sides of my part.
Bolting my custom gadgets directly to the TRT platter ensure they're mounted rigidly, and if a guy has to remove 6 bolts to dismount a gadget and torque up another 6 bolts to mount a new gadget, that's no hardship.

Somewhere in there, is a minor business opportunity for someone, because I cannot believe other TRT 70 and TRT 100 owners haven't confronted this exact same problem.
I'm way past the age where I could contemplate getting something like this up and moving, but somebody could perhaps do a decent small trade in something like this.
Sad reality is you might get 50 sales a year in the first 5 years and then everybody who wants one already has one.
Every serious manufacturer like say a medical jobber, is not going to pin his production hopes on a TRT 100...they want something with way better accuracy specs.
The TRT 100 is only accurate to 45 arc seconds, and that's on a good day!

I'd be curious to see a business case...none of this stuff is hard to build, but it's a real PITA compared to just going to the fixture store and dropping a bit of coin.

Orange Vise...do you have thoughts on this?

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
You can add the now obsolete haasTr110 to your customer list.
Small platter and it is very sensitive to excess stack height due to its 5th platter being way above centre.
Nice little unit otherwise.
 








 
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