Cutting Large Internal Keyways with Sinker EDM?

I have to cut several large internal keyways in some mild steel pieces, the largest ones are 45 mm (1.772"). The parts are 7" long.

I found these for sale;

EDM Machines : 2 complete Cincinnati Milacron Electrojet Cintrojet EDMs Socal.

They are similar in size to this;

Sodick EDM Model Mark A7C RAM Type Die Sinker | eBay

My question is, would this be an efficient way to cut large internal keyways, or would a wire EDM be better? (The sinkers are manual machines)

If it's a blind keyway, sinker is the only option. If the keyway goes all the way through broaching is fastest if feasible
, if not then wire EDM.

Direct answer to your question, no not an efficient way, and would not make you money as part of a manufacturing operation. For a one off job, and you had a sink EDM already, it would get it done. I have done so myself.

Two concerns with the Cincinatti EDM you are looking at.
1. Sounds like it has a hydraulically operated ram, (most modern machines use ballscrew and servo like a mill or lathe) my experience with this type of machine is limited, but in each case led to frustration, the accuracy of motion depends on the condition of the proportional valve, any wear and/or contamination and the ram does not do what the controller wants and you get low cutting efficiency, high electrode wear, arcing, or no operation at all.
2. They say no oil, that may mean hydraulic oil, or EDM fluid. If it has no EDM fluid be prepared to spend $1000-$4000 filling it up, depending on tank size.

If you don't want to sub it out to a wire EDM, a shaper would eat this job, and they are usually cheap, even scrap price, easy to use and no control issues to worry about.

RJT said:

If it's a blind keyway, sinker is the only option. If the keyway goes all the way through broaching is fastest if feasible
, if not then wire EDM.

Click to expand...

I guess that I just need to bite the bullet and buy a wire EDM then. I always wanted one anyway. They do go all the way through, but a 45mm push broach would be really huge...

ADFToolmaker said:

Direct answer to your question, no not an efficient way, and would not make you money as part of a manufacturing operation. For a one off job, and you had a sink EDM already, it would get it done. I have done so myself.

Two concerns with the Cincinatti EDM you are looking at.
1. Sounds like it has a hydraulically operated ram, (most modern machines use ballscrew and servo like a mill or lathe) my experience with this type of machine is limited, but in each case led to frustration, the accuracy of motion depends on the condition of the proportional valve, any wear and/or contamination and the ram does not do what the controller wants and you get low cutting efficiency, high electrode wear, arcing, or no operation at all.
2. They say no oil, that may mean hydraulic oil, or EDM fluid. If it has no EDM fluid be prepared to spend $1000-$4000 filling it up, depending on tank size.

If you don't want to sub it out to a wire EDM, a shaper would eat this job, and they are usually cheap, even scrap price, easy to use and no control issues to worry about.

Click to expand...

That was the information that I was looking for on the sinkers. I am disappointed, but you probably saved me lots of headaches.
I can not find a big shaper. There are a few around with a 6" stroke, but that won't cut it.

the thing to do with the sinker is lay the part sideways and use a long (7" + bar) laying through the bore and plunge into the key from the side not the end so you only cut about 1" of stroke but 12sq in area. (1.77" x 7")

my antique raycaon re20 hydraulic sinker can cut about 1" of depth per hour with graphite. an orbiter would help the speed.

my 1998 robofil 290 wire can profile between 10-20 square inches per hour, but I doubt 7" thick. you have 7" depth by in about 3" profile? 21 square inches? good luck finding a decent running supported wire for under $20k

just 2 data points from some older machines to consider.

bandsaw all you can out if you decide to sink it. make many cuts with a little step over. or at least a pair of v notches then sinker it to clean it up. -If you can weld a blade together after threading through the gear. sounds painfull.





the sinker may be more economical but you need a lot of amps. I think 10 amps or more per square inch.



I remember a thread here long ago about a chain driven horizontal milling cutter for making keyways.

dsergison said:

good luck finding a decent running supported wire for under $20k

Click to expand...

Would you consider this a "supported" wire?

Hitachi H Cut 203M20 Wire EDM Machine | eBay

I ruled out sinker for the most part due to post #3 in this thread...

Hi David:
Short form:
NOPE!!
Hitachi has been out of the wire EDM business for some time, and parts are apparently impossibly hard to get.
The main players these days are:
Agie/Charmilles
Fanuc
Mitsubishi
Sodick
Makino

Other good machines currently sold new and supported are:
Accutex
Chmer
Ona

Brands still serviced to a limited extent by EDM remanufacturers:
Brother
Japax


Most popular brands (means most likely to be able to get help on this forum):
Agie
Charmilles
Mitsubishi
Sodick

Each of these has strengths and weaknesses; one of the more challenging decisions you'll face is which one has the most desirable combination of characteristics for YOUR applications,especially since many experienced guys have very strong preferences and are not shy about articulating them.
For jobbing; especially with bigger stuff I'd want:
1) Submerged machine
2) Tall Z axis capacity and big tank
3) Simple to run
4) Cheap to service
5) Reliable autothreader
6) Adequate precision
7) Decent speed

Notice how I said "adequate precision" rather than "super dooper dead nuts precision".
The reason is that most new or well maintained wires can cut far more accurately than most shops can even measure, and most jobbing type work is more than adequately serviced with a machine that can consistently be made to cut within 0.0005"
Without an investment in climate control and metrology, extra money spent on the finest accuracy you can buy is wasted money in my opinion.
Cheers

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining

I'm no expert. but I have shopped and purchased wire edm's recently, and a running supported machine worth owning is $20k not $6k.

no oil means no edm oil. high grade full synthetic is $1000 per 55gal drum. lower grade stuff much cheaper. 1/2 to 1/4 that cost I think.

I bought a "said to be running when taken out of service" hydraulic sinker for $2k. from I a guy I met on this board. It was a shot in the dark I could afford to risk. I was naieve, but I lucked out. I made my money back in a weekend.

great post here
http://www.practicalmachinist.com/vb/edm-machining/does-used-sinker-edm-make-sense-219076/

and rough that material out mechnically if at all possible!!

dsergison said:

I'm no expert. but I have shopped and purchased wire edm's recently, and a running supported machine worth owning is $20k not $6k.

Click to expand...

Sounds like new is going to be the way to go. There is a tool show in Greenville, S.C. in October and I am already registered. If I see something that I like, I might be a potential buyer...

David another customer of mine who is local to me is also talking about buying one for his use. Perhaps if you get one he can send work to you or if he gets one you might want to let him cut for you? I know he wont keep it busy full time, so it might be a question of which one of you gets a machine first...

Charles

Hi David:
If you're considering new, have a close look at the Chmer machines sold by EDM Network.
I'm very happy with mine, now that it's early teething troubles are dealt with (some minor problems with the threader and some interesting challenges getting it to talk to the aftermarket rotary axis, all very competently solved by Larry Macnamee, Larry Wetmore and Joel Neilsen from EDM Network)
It's a mid-range Taiwanese machine with glass scales; very simple to run, accurate, fast and built very solidly.
I spent about 120K including the rotary for the smallest model in July of 2011.

If you reconsider and go for used, Charmilles seems to be the bulletproof brand most often described as too tough to break.
If it wasn't non-submerged, I'd be thinking a Robofil 510; nice big capacity and 15" in Z I believe.
Cheers

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining

CBlair said:

David another customer of mine who is local to me is also talking about buying one for his use. Perhaps if you get one he can send work to you or if he gets one you might want to let him cut for you? I know he wont keep it busy full time, so it might be a question of which one of you gets a machine first...

Charles

Click to expand...

I'm thinking that maybe I should have bought that Charmilles that was in the garage in F.B. Ga. Especially after reading post #12...

implmex said:

Hi David:
If you're considering new, have a close look at the Chmer machines sold by EDM Network.
I'm very happy with mine, now that it's early teething troubles are dealt with (some minor problems with the threader and some interesting challenges getting it to talk to the aftermarket rotary axis, all very competently solved by Larry Macnamee, Larry Wetmore and Joel Neilsen from EDM Network)
It's a mid-range Taiwanese machine with glass scales; very simple to run, accurate, fast and built very solidly.
I spent about 120K including the rotary for the smallest model in July of 2011.

If you reconsider and go for used, Charmilles seems to be the bulletproof brand most often described as too tough to break.
If it wasn't non-submerged, I'd be thinking a Robofil 510; nice big capacity and 15" in Z I believe.
Cheers

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining

Click to expand...

Marcus, thanks for the advice. When I do finally purchase something, I will post some pictures.

implmex said:

If you reconsider and go for used, Charmilles seems to be the bulletproof brand most often described as too tough to break.
If it wasn't non-submerged, I'd be thinking a Robofil 510; nice big capacity and 15" in Z I believe.

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining

Click to expand...

Marcus, I found this yesterday;

Charmilles Robofil 6000 CNC Wire EDM Machine | eBay

It looks quite old, and does not appear to be running. Also, seller has no feedback.

MECHANICALLY!

If what you really NEED is to make keys, buying one of these (or making a similar chain driven unit) will be a lot easier than buying and fixing a <$20k wedm.

National Machine Tool
National Machine Tool Company ,cincinnati (usa) - Contact Information

the drive mechanism on those is weird but they work I guess.
I have seen a shop made version that drove a standard horizontal milling cutter with a chain and sprocket.

dsergison said:

REMOVE MECHANICALLY!

If what you really NEED is to make keys, buying one of these (or making a similar chain driven unit) will be a lot easier than buying and fixing a <$20k wedm.

National Machine Tool
National Machine Tool Company ,cincinnati (usa) - Contact Information

Click to expand...

I understand that.. but a wire would give me so much more capability, and since we are a job shop, I'm hoping that I would pick up some work that I would normally have to pass on or sub out. (Subbing work out is usually a pain.)

I Understand,
I bought one of these, I would not go any older, or much cheaper. mine was actually 16k, not actually "demonstrated good running" but it was a crap shoot and I have had to do a fair bit of fixing, luckily no expensive parts were needed.

1998 Charmilles Robofil 290 CNC EDM Wire Cutter | EDM Wire Cutting | CuttingMachineryLocator.com

dsergison said:

I Understand,
I bought one of these, I would not go any older, or much cheaper. mine was actually 16k, not actually "demonstrated good running" but it was a crap shoot and I have had to do a fair bit of fixing, luckily no expensive parts were needed.

1998 Charmilles Robofil 290 CNC EDM Wire Cutter | EDM Wire Cutting | CuttingMachineryLocator.com

Click to expand...

Looks good. With z-axis travel at 9.8 inches, it would have no problems handling an 8" tall part, correct?

Hi David:
Old beater machines regardless of brand are a real crap shoot especially if either or both of two things are true:
1) You're not an electronics guy
2) You don't have time and resources to fart around fixing one of these things up.

I recognized early that both constraints apply to me, so I went with a re-seller of repaired equipment and invested around 40K for a reconditioned Sodick A320.
I gained the following:
1) Training to make me productive right out of the gate.
2) A machine that was known to be running when it was delivered, had a warranty, and was supported.

In spite of those advantages, I still had my share of breakdowns resulting from the fact that it was a machine run for a very long time (since 1996) in the harsh environment that wire EDM's must operate in.
BUT: whenever the old girl crapped out, I had a way to get her fixed; reasonably promptly, reasonably inexpensively, and reasonably reliably.
I also had a guy (Larry Wetmore) to help me with questions about programming, machining strategies; the whole nine yards
That to me was worth every penny of the high purchase price.

I ultimately knocked up against the limitations of that purchase (accuracy mostly, but also limited capacity, increasing breakdown frequency, and no autothreader).
So I pulled the trigger on a new machine, swallowed my terror and dropped the cash.
What I have now is an order of magnitude better than what I had then, so again, it's been worth it by my calculus for my situation.

Moving on to other aspects of the machine:
The single biggest reason I have to NO BID on wire work that comes to me is insufficient Z axis capacity.
I didn't have room for anything bigger than what I bought and I specialize in small complex stuff anyway, but if you're jobbing, your capacity will be a real advantage.
Lots of guys can do 8", a quite few can do 11", few can do 15" and I can think of only two who can do 24" or bigger.
So I, like many others, must refer tall work out, and you could be one of the few to capture that kind of work if you invest in the capacity.
It's a great way to generate business, and there are no workarounds; if the stuff is too tall to go between the wire guides, it can't be wirecut on that machine, no way no how.
For jobbing, buy lots of Z axis capacity...more than your competitors have; it's worth it!!
Cheers

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining