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Fixture for round parts - VMC - newbie questions

Wade C

Stainless
Joined
Jul 21, 2004
Location
Wiggins CO. USA
Im new to VMCs, and finally getting done with various maintenance and cleaning on the new to me Fadal 4020HT (88HS, Rigid Tap, 10k Spindle, 28" Z - for reference)

Im starting the learning process on fixturing, setting up, accuracy, etc. Im not well versed in multiple part fixtures because until now, its all been turning center work, or running singles on the manual mill. But now with the magical "tool changer" contraption on the new to me VMC... and increased demand for some of my products, its time to start thinking more about efficiency and output and get this critter humming. Not to mention learning more about everything in general in the process.

Im starting my learning with a fixture for holding an ≈8" long by .625" round, water hardening drill rod (from enco), and I need to cut three "flats" or "slots" across it - all on the same "side" - like a flat for a set screw on a shaft.

I wanted to pick some brains about fixturing ideas if anyone is feeling generous with their time.

I would like to be able to hold maybe 10-20 of these at a time. I have to cut one slot 1.040" wide (+/-.025") that is .124" deep (-0/+.002") in the middle of the 8" long rod, and one end (within 2" of the one end), there will be two slots each .500" wide (+/-.025") and .070" deep (+/-.025"). Positioning accuracy is +/-.025". Basically one slot is important to functionality (slot depth is the major factor), the other two just need to be there, location of the slots does not have tight tolerances.

Im probably over thinking this... and worried about nothing, but thought best to get good advise before I plop down a chunk of change for a block of material to cut the fixture into. To complicate things (maybe) I will be later doing very similar parts in different diameters up to .875" dia.

Here are some of my initial questions: (main concern is keeping the -0/+.002 tolerance on the one slot across all the parts)

Material Choice for Fixture:
Steel? Aluminum? cheap Chinese mill vise body (I have a couple laying around and two Kurt 675s on the way to replace them)?

Type of cuts in the fixture for best hold and locating of part and clamping: -Fixture face milled flat on bottom portion, and a top clamp the parts down with a "U" flange of some sort?
-Cut sort of a "V" into the bottom portion, and a flat clamping bar across the top
-5/8" holes drilled through a couple blocks, and then set screws into each bore (drill/ream blocks and mount so holes are parallel to the table) - I suspect this to be the lease accurate way to do it
-Some other methodology I am obviously missing because I didnt mention it?

I can see some potential head aches for all of these methods, and I know it will be a learning process - teaching my self to make the fixture, and then how to remove it from the table and accurately reinstall it at a later time. But I dont have the experience to know which headaches will be a big deal, and which ones are easy to overcome. Id like to think Im not stupid, but KNOW Im VERY inexperienced.

I hope I havent wasted everyones time (and made you regret reading this post)... Im just getting my feet wet on the VMC side of things, and trying to avoid some of the usual stumbling stones... er I mean learning stones that i tend to easily trip on.

Thanks for reading and thanks in advance for your patience and help.

Wade
 
Check out miteebite.com especially their uniforce clamps.

You should allways make your fixtures out of something harder than what you will be holding in them or they will become indented or wear out. A fixture for drill rod should be made of something that you can harden. Perhaps an 1/8" insert that can be screwed in for .625 dia and removed for .875 dia.

Good Luck
 
Id just clamp a thick piece of aluminium down and mill as many V groves into it as you can fit leaving allowances for 3/8 taped holes between some of the groves which you could use to hold large straps to hold all the bars down.

the 4020 has 10+ inches of travel in the y right? if so you could gang up an easy 30-40 if you really wanted to


HOWEVER

if your just milling 3 flats all on the same side of the bar, id just do one at a time. Its going to take longer to load it in a fancy multi part fixutre than it will take to mill the part itself.
 
What kind of quantity per run or per month are we talking about?
Not a lot... I probably sell 5-10 a month tops... but would probably try and run around 50-100 at a whack just to not have to constantly be setting up and tearing down.

Check out miteebite.com especially their uniforce clamps.
Very interesting idea... good theory to learn from for reference any one way or another. Thanks!
The drill rod is not hardened, so maybe hardened fixture is not that necessary?

Id just clamp a thick piece of aluminium down and mill as many V groves into it as you can fit leaving allowances for 3/8 taped holes between some of the groves which you could use to hold large straps to hold all the bars down.

the 4020 has 10+ inches of travel in the y right? if so you could gang up an easy 30-40 if you really wanted to

HOWEVER
if your just milling 3 flats all on the same side of the bar, id just do one at a time. Its going to take longer to load it in a fancy multi part fixutre than it will take to mill the part itself.
Aluminum idea was one I was kicking around... figuring if it wore or something, if I got enough material, I could reface and recut to compensate for wear if there was some just didnt know if it was a "smart move"

The 4020 is 40x20 travels. Im sort of thinking, considering the current stuff I have to run, that I might be able to set up the fixture and leave it for a while... though a good sign would be be having to tear it off to put more - other work on the table :D

One at a time... Ill have to think on that approach... maybe setting up the two kurts, and just run two at a whack and bust em out in stead of bolting a batch down, run for a few minutes and swap out... One of those things where maybe one at a time is just as fast or faster than fixturing up 10-20 at a whack to run twice and be done for a few months.


Great input! Thanks so much, and keep it coming! Im trying to absorb as much as I can!

Wade
 
For 100 parts I wouldn't bother with a big fixture plate on a subplate. Too much expense and time in design/building the fixture...it would take forever to pay off at those quantities, especially if you make 100 parts, sell 10/month so you'll only be setting up once every 10 months.

I think you'll be money and time ahead to just make some steel soft jaws (for your Kurt vices) that have a groove in them parallel with X (just like a V block) to locate the parts in Y and Z. Cut the parts long and eyeball their placement in X so you don't have to mess with work stops, then machine them to length. Make the jaws 7.975" long or so. You'll be done with making the jaws AND the parts before you can think about making high density fixture plates.

The jaws will eventually wear, but not for a good long while. It will probably be cheaper to just make new sets when the time comes versus making the jaws out of something heat treatable and having them heat treated.

Like the guys here say, sometimes the best way to make something is to just make it.
 
One at a time... Ill have to think on that approach... maybe setting up the two kurts, and just run two at a whack and bust em out in stead of bolting a batch down, run for a few minutes and swap out... One of those things where maybe one at a time is just as fast or faster than fixturing up 10-20 at a whack to run twice and be done for a few months.

I'd probably do one or two at a time since you're only making low quantity and it's a fast operation with no tool changes. Sometimes you just have to put your head down and get the parts cranked out.


Theres nothing worse than some guy spending 19 years dinking around with a fancy fixture and talking, and screwing around, and taking breaks. Wow, sure saved a lot of time with that fixture:rolleyes5: Could have been done 3 days ago if you'd just got in there and pounded the parts out. Stay on task, keep your head down and get done. :cheers:

Edit: I was writing my post while matt was posting his. Do what he says. 100% right on.
 
The other way of looking at it is.

Can you make and load a fixture in the time it would save

EG;- Let's just say it's 1 minute to stop spindle from cutting, open vise, unload, load and restart spindle to cutting (don't forget doors openening and closing on a CNC)

100 parts = 100 minutes.

Can you make the fixture, load & unload the required number of times to do the run of 100 in less than 100 minutes? - or 1 hr 40mins from which has to be subtracted the cost of the fixture material?

If you can't, could it pay off over say 2 batches? which in this case is about 2 years,........... IME any longer wouldn't be viable.


An aside;- With fixtures you have to take in to account Sods law and Captain f'k up joining forces,...... by changing the design or taking the job going away.
 
If you had a double sided vise you could run two of them at a time. that would be pretty quick. If you dont have one you could problbly pick up a used chic vise for a hundred bucks of so
 
Thanks for all the advise! Ill run it through my head, think on the time investment on the fixture vs part run vs profit... I may end up making something anyway, merely as a learning experience. Being completely new to the VMC side of things, it might be some "smart time" spent... not for the outcome, but the process and effects of what and how I do things.

But I can really see (but hadnt really thought of) the "just do it" approach, in terms of just throwing one in a vice and cut it, and keep feeding the beast.

I really appreciate it!
Wade
 
I really like that idea! Never thought of separators like that to run multiples in a vice.
It's a great idea. Just be careful with making all the spacers the same height if you're going to try to run more than 2 parts in a vice, or I would think you'd have a nightmare of floating Z heights on the center part that you wouldn't really be able to hammer down on the vice to sit correctly. If you use spacers like that, maybe make one long one, then saw to width so they are all exactly the same?

I might be over thinking that one.
 
I was sort of wondering about that, but was giving it time in my head to rattle around before I asked more questions :D

But I too was thinking about making it in a single bar and cut into segments.

Wade
 
Yes, I definitely suggest making it out of one bar and slicing off. You could harden and precision grind the V's then use a wire to slice em if you are so inclined. A bit more expensive that way, but they should last a long time if you do..
 
I won't argue with the voice of experience that says "just put 2 or 4 or whatever vises on the table and run the parts".

UNLESS

You could be doing something else at the same time as these parts run.

So there, the math isn't "can you make a fixture in 100 minutes to save 100 minutes" - but rather "can you make a fixture in 200 minutes that will let the machine run *unattended* for 200 minutes while you do other work elsewhere?"

-> Parallelism!!!

Now of course, if there is no other work, or you don't have enough power to run both machines, etc. etc., never mind.
 
If you had a double sided vise you could run two of them at a time. that would be pretty quick. If you dont have one you could problbly pick up a used chic vise for a hundred bucks of so


Wow, let me know where you can find even the older chick double vices for $100. I never ever see them for less than $600 - $800.
 
When I 1st got into CNC mills...I went with fixtures, making sure I ran two plus parts at a time. Second and third vises...multi-part fixtures the whole gamet.

As time went by and the jobs came up again...I saw my fixtures and realized had I done it a bit different I could save some time....many of the old fixtures and elaborate setups went by the wayside as I leaned more and more.

Other fixtures I had zero issue with when I ran them...soon as I put new hands on the job, the fixtures didn't work so well anymore...some need revamping and others I just realized cost too much to remake and no longer worth it.

While a learning experience I wouldn't trade, as I learned alot along the way which I can fall back on today...alot of what I did mostly impressed me...customer didn't care as long as his parts where done correctly and on price target...and for me the bottom line was did I make money and how much....somewhere I realized the KISS method is more often then not the best way.

That said I am a big fan of soft jaws and multivises...quick setups and teardowns and the jaws become your fixtures. If you watch your chips they can last a long long time.
 
Wow, let me know where you can find even the older chick double vices for $100. I never ever see them for less than $600 - $800.


E-bay, about 3 years ago I got a Chick 4" Bi-Lock for $46. Looked like it had never even been bolted to a table, but had been sitting in the corner for 10 years. Of course they never put the word Chick anywhere in the listing, I don't even think it said "vise". If it had been listed properly it would have been much more.

Searching for mis spellings or just search the whole metalworking category. I got a nice Cannondale a while back as the only bidder. They didn't put a space between Cannondale and the model #, so anybody searching for a "Cannondale" never saw it. They were going for $5-$600 and I got it for the starting bid of $180. Guy was pissed didn't want to ship it.

Back to the fixturing stuff. I find it amazing how much work can be done in a vise. Stuff that 8-9 years ago I was making fixtures for. I don't make a whole lot of dedicated fixtures anymore, and the ones I do make are WAY better than the ones I made years and years ago.

Piles and piles and piles of soft jaws.
 








 
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