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Rotary fixture to accommodate wide range of parts

barbter

Diamond
Joined
Oct 27, 2007
Location
On Tour...
Fixture as drawn, will ring like a church bell.
Nowhere near the overall stiffness IMHO, and you'd need a more substantial tailstock.

The trouble with long fixtures, when you need perfect flatness, is on setup you can easily get a few though error in the tailstock which then may produce your worry of groove depth etc.
You can counter that of course by having separate datums for each part - so the Z datum of the tailstock end fixture would be slightly different to the other nearest the rotary.

Looking at this....my gut feel would be an aluminium fixture making 4 at a time (side 1 Rotor side 1, Side 2 Rotor side 2).
Probably 70mm thick (so made from 3") and pocketed in the right areas to remove weight, but retain strength. Steel ends (rotary and tailstock for wear).
Then I would attach to both top and bottom (the flat sides) ground flat stock (B01).
Use these as sacrificial wear strips, so when a rotor is dropped it beats the (replaceable) wear strip, and not damages the main fixture "body".
These would need to be say 10mm thick minimum, and can be located into the ally fixture body using a couple of dowels and csk screws to retain..

Then for Rotor location....If I read right, the OD's are within a few thou.
So I'd look to use that for "rough" location.
Have a grid of location pins as the attached, which will give you say 10 thou clearance on rotor diameter (use modified shoulder bolts and use the head as location).
Then have 2x slide top clamps (left to right) to clamp.
And cycle start probes the OD (and top) each time and sets datum accordingly.

And for the next size Rotor, move the 2x dowels "inwards" to the new position (fast changeover).

Worth laying it out on the CAD to see if it'll work, but I'm sure it will.
 

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Fadriver

Aluminum
Joined
Apr 24, 2011
Location
los angels ca.
We've always been getting castings made in the US.
We have several custom castings that we are able to get 100s of different rotors out of. That's part of the problem with all our fixturing is everything is similar, but just different enough we can't have anything truly universal, but were pretty close. Two piece rotors add to complexity because there's no bell to help maintain rigidity and rotors like to warp, another reason they aren't finished on the VTLs.
If we only made a couple different parts it would be easy to buy a brake specific machine and crank them out, but because we have such a high mix wed spend more time setting up and tearing down than actually making anything. I see them for pennies on eBay and think about how to make it work constantly.

Lathe drilling wrong approach, that is mill op, and a slave foreman at the floor, its that way done
correct me if wrong drilling and grooves are R&L ,they use g51 mirror and even chamfers done with electric hand drill with stop adjustment while mill drilling and grooving operator is chamfering holes
its not automated just labor intensive, guy next to me drills up to one set 4pc. lot. 3 jaw chuck with
stop in vanes for timing, 15 yrs ago he offer me $6.50 a piece so i said let me think about it, and stop chasing the job.
 

GiroDyno

Aluminum
Joined
Apr 19, 2021
Location
PNW
I think your proposal is too complicated and too slow

20x40 VMC should be able to hold 4 parts, 2 off every cycle. [edit] OK maybe not for 16 inch discs]
Seems pretty simple machining, so your toolchanger is probably not full for any good reason. Means a right angle head could do the engraving on the edge rather than spinning the whole thing. But still even 16 inch diameter, 4 hub centric fixtures and you could probably still fit 4 in the flat and 2 on edge a the end of the table, if you have a 40x20x20.

12 clamps to open for 4 parts, parts oriented A-B A-B left to right[for instance] 2 discs held vertically at the right end of the table by a previously machined bolt hole, defining the height for engraving. A simple clamp again can hold two discs at the right since the location of the text is non critical.

Truthfully 10 parts on order for a stock part does not mean making 10 parts. It is usually cheaper to run them and hold them. Sure sometimes but if it is your product I think you will make more money by cutting lead time than saving shelf space.

Truthfully a lathe with live tooling would probably be the thing to do. Once it is on a machine let the machine to the work

A live tool lathe wouldn't produce finished parts, we cannot cut the ID flange because we use the turned geometry for holding in the last op to twin cut the faces.

Unfortunately the only way we could fit 4 parts would be if they are 12" OD or less which is less than 10% of our parts. If we went out and bought a 50" that grows to 13.5" OD and 25-30% of our parts.

A mag chuck and centric locating features (what we already have) seems faster to me than 12 clamps.
But I do like your workflow suggestion loading a rotor sideways to skip an offline process, it doesn't actually reduce any handling but would be a step in the right direction if I can't make a one-and-done fixture work.

We don't have spare space, time, or castings to machine excess stock inventory. Right now we are trying to design processes that will boost production enough to keep up with sales, so that we can have the spare time and resources available to make stock inventory.
 

barbter

Diamond
Joined
Oct 27, 2007
Location
On Tour...
Obviously live tool lathe gets you more towards "off in one" and thus reduces handling, but also slows throughput unless you have more of those machines....
What size are your vmc's you currently have?
Your largest discs x 2 side by side are 820mm, so an X travel of 850 would be able to accommodate but you couldn't then do left to right clamping - you'd have to have 45 degree (more front to back if that makes sense).
The Chevalier's I had were 850mmX and 520mmY and a compact footprint.
Then for the rotary and the tailstock, you just have to mount them outside the travel like the attached
 

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Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
Obviously live tool lathe gets you more towards "off in one" and thus reduces handling, but also slows throughput unless you have more of those machines....
What size are your vmc's you currently have?
Your largest discs x 2 side by side are 820mm, so an X travel of 850 would be able to accommodate but you couldn't then do left to right clamping - you'd have to have 45 degree (more front to back if that makes sense).
The Chevalier's I had were 850mmX and 520mmY and a compact footprint.
Then for the rotary and the tailstock, you just have to mount them outside the travel like the attached

I'm surprised you're supporting all that with that dinky little lathe center. I don't think that tailstock is doing much for you.
 

barbter

Diamond
Joined
Oct 27, 2007
Location
On Tour...
I'm surprised you're supporting all that with that dinky little lathe center. I don't think that tailstock is doing much for you.

MT2 centre with the point removed and the angle seating 90% into the steel end of the fixture.
Tailstock was quite substantial and never was a problem.
Haven't got a piccy to hand of it, but it's virtually the same geometry as this one (also MT2 etc)
 

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GiroDyno

Aluminum
Joined
Apr 19, 2021
Location
PNW
Is there a rule of thumb for fixture thickness vs span? Or do people just eyeball it?
Adding a middle support between parts would probably help reduce fixture deflection, but nobody chimed in to clarify if its the fixture that needs to be "stiffer" or the clamping method...

I took a CAD model of a 9x35" stock trunnion and modified it to fit some centric grippers and a pair of 16" rotors. Using Fusion360 I ran a quick analysis. The stock trunnion in cast iron had .0001" max deflection, using the same parameters on my modified design it showed .002" deflection (so .004" total with a flip) which doesn't seem too horrible, especially considering I switched it to 6061. Spending more than 15 minutes designing it, or just switching to steel could cut that in half which would be acceptable.

deflection.jpg

I'm no stress analyst, so I'm not going to bet my life on this but its a little confidence inspiring.

I know Schunk makes both robot grippers and pneumatic vises, are those grippers capable of holding parts for machining? They have longer strokes than a lot of the pneumatic 3 jaw chucks I see which would help cut down on jaws, using a step in each set of jaws to do 2 sizes I could make 5 sets of jaws to cover the entire range.

Just Googling for comparisons I found this Precision Stationary (Milling) Air Chuck 125mm chuck has 970 KGF and 3mm stroke
A Schunk PZN 125 has 3330 N and 12mm stroke. According to Google that would only be 340 KGF, but it would only require 1/4 as many jaws.

PZN 125 specifies a workpiece weight up to 15.5kg, that's quite a bit more than the largest rotor.
 

mhajicek

Titanium
Joined
May 11, 2017
Location
Minneapolis, MN, USA
Yeah, I eyeball it. It's served me well so far. .002" chatter will wreck your tools, and that's a static calculation; dynamic harmonics could get much worse.
 








 
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