opinion; old German milling machine

Discussion on all milling machines vertical & horizontal, including but not limited to Bridgeports, Hardinge, South Bend, Clausing, Van Norman, including imports.

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John Evans
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Re: opinion; old German milling machine

Post by John Evans »

The highest speeds will only be useful running small endmill type cutters . If you want to run say a 6" slitting saw or a 3/8 wide 4" wheel cutter in steel you will want the slowest speeds. grind off the damaged teeth so they do not make contact and run both available speeds in that range box. Keep the 2 speed motor ,forget the VFD . a 3 inch diameter at a little over 100 RPM is 100 SFM which is as fast as a HSS cutter in mild steel should go for normal work. This way you will still have 12 speeds and a much better chance of having a usuable speed range. Personally I would carefully inspect the gear the bad one mates to for any damage and if it is good to use buy the damm new expensive gear if the free one does not happen. That mill looks to be too capable to do a bodge to make it kinda usuable !! When I had my SAJO horizontal I rarely ran it over 500 rpm using wheel style cutters and most of the time much slower. again you need to check surface speed of you cutter !!!! Even on my Bridgeport I rarely run over 1500 unless under 3/8 dia end mill in steel. Aluminum is another story you can hardly go too fast.
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John Evans
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Re: opinion; old German milling machine

Post by John Evans »

Mark: You posted your speed break down while I was typing and extended reply. And the answer is keep the low speeds buy using your rotary converter and both motor speeds. 2000+ RPM will be fine unless you plan to do a lot of aluminum with under 1/4 endmills. With wide wheel cutters a horizontal mill is a metal eating monster ! LOL But, these need the appropriate SFM = low RPM.
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John Hasler
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Re: opinion; old German milling machine

Post by John Hasler »

Are the vertical and horizontal spindle speed ranges the same?
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liveaboard
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Re: opinion; old German milling machine

Post by liveaboard »

Yes, the vertical + horizontal are the same.
I can keep the low, and keep the high too, and just have 12 graduations instead of the original 18.
With tax + postage, that part will cost $500, and the gear it rides on could be damaged.
Bear in mind the entire machine with transport only cost $2,500.
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Bill Shields
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Re: opinion; old German milling machine

Post by Bill Shields »

You will be surprised how often you need low speeds with high torque pushing a big cutter...esp on a horizontal mill.

I would be very cautious about running the motor at 50% rated speed or less. Many older motors do not react well to low speeds and high torques.

Keep in mind that many vfds do not like having the circuit between the electronics and the motor interrupted.. which means that you start and stop the motor at the vfd not on the mill control panel.

You will also need to handle the coolant pump with another VFD unit and come up with transformers for the relays and coils on the clutches.
Too many things going on to bother listing them.
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liveaboard
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Re: opinion; old German milling machine

Post by liveaboard »

The motor is a dual speed, it's made to run at 2800 or 1400.
Rating at 2800 is 1.5kw, at 1400 it's 1.1kw

At 1400 motor rpm, spindle can be geared down to 45 rpm.

If I use a VFD on the spindle motor, I would leave the other motors, transformers and rectifiers, as they are. Why would I need to change them?
The spindle motor wiring would be changed to only run on the high speed coils. At 25hz, it would still be within it's original power/ speed rating.

I think 45 rpm is low enough?

It would be a simple matter to repurpose the old motor relay to switch the vfd control circuit.
I could even rewire the old switches so that they would instruct the vfd to 1/2 motor speed where the motor used to be switched to the low speed coils.

But as I said above, right now I'm leaning toward just putting it back together and using it as is.
The broken gear means 1/3 of the ratios are not available, but it still has 12 speeds from 45 to 2240.

There are some missing pins in the complex gear selection box.
I think someone removed them, to try and block off the broken gear.
If so, it was a mistake; the missing pins were for one of the working gears. It's a complete mix up.
The other possibility is that the pins fell out and that caused the damage when the change gear wasn't locked in place, and ran on the corners of the teeth.

I don't see how the pins could fall out though, and they're not in the bottom of the box. Also, that scenario would result in damage to the counter-gear that I don't see.

It looks to me like someone attempted to do what I'm doing, but bodged it up, and then it was sold 'as is', probably at auction because it's missing things like the crank handle for the spindle drop.

Which is how it came to be sold at a price I could pay.
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Bill Shields
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Re: opinion; old German milling machine

Post by Bill Shields »

Ah...so you already have 3 phase power available and are not going VFD to make it. That is good.

Running a dual speed motor on low speed windings is very different than running it at half speed on a VFD.

THINK ABOUT how a dual speed motor works...number of poles used in the stator.as opposed to what the VFD does.

The resultant output speed may be the same and maybe the torque the same.. but the heat generated in and by the motor is very different...generally the low speed VFD configuration makes more heat.

I am not saying it will not work. Just suggesting that you not dive in blindly assuming it will work without a bit of testing.

Would think that a couple of temperature probes on strategic places of the motor would give you data to confirm motor health.
Too many things going on to bother listing them.
John Evans
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Re: opinion; old German milling machine

Post by John Evans »

A bit confused here ,if you have 3 phase power available why the VFD ?
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liveaboard
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Re: opinion; old German milling machine

Post by liveaboard »

Because you guys are dispensing advice without reading the thread.

1; I've decided NOT to use a vfd on the mill, because it will work ok with 12 gears instead of 18.

2; I do have a VFD on my lathe, a 2 speed motor set to run only on the high speed coils, the VFD is 3-phase in, 3-phase out.
The reason is for speed control, and I'm very happy with it.
John Evans
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Re: opinion; old German milling machine

Post by John Evans »

Well I have read the thread but,with the length of same and my advancing age I forgot you have 3 phase to your property. That is so unusual here in the US that we don't think of Europe etc. having residential 3 phase normally available.
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liveaboard
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Re: opinion; old German milling machine

Post by liveaboard »

It's ok, I know you all mean well.
I've been rambling a lot, first I was getting a replacement gear, then I was going to use a VFD to replace the gear, then I decided to just let it work with 12 gears instead of 18 and run it "natural"

Today I fixed the change box, it was missing a couple of push pins and that caused things to go wrong.
Possibly it even caused the gear crash, but probably not. I think there were some bodged repair attempts.

I made the 2 long pins; they press in, 5.1mm
ruhla 250 710 gear selecter box push pins.jpg
Pressed with a clamp + hammer. went ok.
ruhla 250 710 gear selecter box push pin install.jpg
All the positions tested, the lock plate opens + closes and all the shift levers go where they should go.
The box is cast iron and I can barely carry it.
ruhla 250 710 gear selecter box3.jpg
John Evans
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Re: opinion; old German milling machine

Post by John Evans »

I'm somewhat amazed that as nice as that gearbox looked otherwise inside that the one gear died. I think you may be correct that one pin came adrift and let the one gear mis -mesh into the other.
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