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Building a High Speed Punch Press

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randyc

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I thought that you were going to make it on manual machinery. CNC is cheating for a hobby forum, ha-ha. Nice work !
 

JimDawson

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I thought that you were going to make it on manual machinery. CNC is cheating for a hobby forum, ha-ha. Nice work !
I didn't have the heart to tell you last night. It only took about 55 minutes to run the part. It would have taken hours on a rotary table. Thank you for the kind words.
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Now for the next operation, I have cut the keyway in the bore of the cam (pictures to follow). How am I going to get the setscrews exactly on the key center line?

Anybody have an idea?

Hint: I already have the fixture built.
 

randyc

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I'm not sure what set screws you are referring to but if they are used just to apply clamping pressure to the key, then the location should not be all that critical, right ? BUT if one is finicky, LOL, place a length of key stock in the keyway, clamp the cam in the mill vise with the keystock resting on the top of the vise. Indicate one edge of the key stock, move over half the width of the key and drill/tap.
 

randyc

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You ARE going to post a video of this monster-munching-machine in action, right ?
 

randyc

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Jim, I don't know why I haven't asked this earlier, LOL, but why a stepping motor ?

The only reason that occurs to me is that the same motor is coupled to an automatic feed mechanism. The speed of moving work through the press can be adjusted and also momentarily paused for the stamping/punching process.

The stepping motor could presumably adjust the feed without losing a ton of torque. Care to elaborate or is this proprietary information ?

I am REALLY interested in your project because I designed a (much, much, much slower) small punch press in the early seventies to cut microwave transistors from their long lead frames. I used a mechanical means of pausing the work during the punch because high torque steppers were a thing of the future.

(I worked at Fairchild Semiconductor, Microwave and Optoelectronics Division in Palo Alto. Good times !)
 

JimDawson

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Jim, I don't know why I haven't asked this earlier, LOL, but why a stepping motor ?
Good question! There were several considerations.

One of course is high torque in a small package at low RPM. The stall torque is about the same as a 3HP squirrel cage motor, and it will run at that torque all day long. In this case, it will only reach peak torque about 1% or less of the rotation so the motor is idling most of the time. It only needs to run at maximum of 600 RPM, and most likely will be used at about 200 RPM or less. The customer only thinks he needs the higher speed. In order to get this performance curve in an induction motor would have required about a 1.5HP motor, a VFD, and a 5:1 gear box or a special low speed motor. Over all the drive package footprint would have been huge compared to the stepper. It would also have required a 230 VAC supply and that is not available. The stepper is a 15 Amp, 115VAC system, per the customer, I was limited to 20 Amps of 115VAC power.

Cost was also an issue. Purchasing all of the above hardware would far exceed the $420 cost of the stepper motor and driver/power supply.

In the case of a jam, the stepper motor will decouple under excess load and cause no mechanical or electrical damage. In addition the output torque can be limited by adjusting DIP switches

There is no direct coupling between the motor control and the feed, and the motor is not under computer control. It is being run from a pulse generator to provide the step and direction input. It is just a variable speed system with no positioning control except the stop-on-top limit switch when the operator releases the run button.

In this case a missfeed will not cause an issue, the operator will just stop and clear the work area.

I looked at a lot of options, including pneumatic, electrical solenoid, and induction motor, for driving the press before I settled on the stepper.
 

randyc

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Thanks for taking the time to explain, Jim.

It is obvious that you put a great deal of thought into this project and examined MANY considerations as a good designer should do ! I hope that your customer appreciates the depth of your concerns/solutions and that he is adequately compensating you for both your ingenuity AND your craftsmanship !

I'm a little puzzled about the fact that the punching operation is de-coupled from the feed and nothing is under computer control. Have you included some form of limiting mechanism to detect the proper positioning of the workpiece under the punch ?

But I am thinking of two or more operations where features that are punched must be aligned with one another. I'm beginning to infer that it does not matter (e.g. punching out washers or something, where there is no need to align the punch with a workpiece under it).

Don't want to be a pest but I wanna' see that sucker run (and understand how) ! I realize that there is a proprietary concern, of course :)
 

JimDawson

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I can tell you that this is a hand fed, cut-to-length operation. The parts are short and are fed to a hard stop, hence the need for maximum open time. The operator only has to keep some pressure on the end of the material as it is cut on the other end. Ultimately I will completely automate the process, but the customer is not ready for that step at this time.

If this was a progressive operation I would be doing things a lot different. I have a strip out of a progressive die sitting here on the table, it has about 20 stations and 14 of them actually perform an operation. I just got that one back together the other day.
 

randyc

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I can tell you that this is a hand fed, cut-to-length operation. The parts are short and are fed to a hard stop, hence the need for maximum open time. The operator only has to keep some pressure on the end of the material as it is cut on the other end. Ultimately I will completely automate the process, but the customer is not ready for that step at this time.

If this was a progressive operation I would be doing things a lot different. I have a strip out of a progressive die sitting here on the table, it has about 20 stations and 14 of them actually perform an operation. I just got that one back together the other day.
I get it ! Thanks -
 

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Here is the first test run without the front bearing housing and covers. Also my first real movie here!!!!!

 

Tony Wells

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Nice work, Jim. Curious about one thing. Wondering how you addressed the physics of all the moving parts. At the speed it will operate, the moving parts possess enough mass to be considered in terms of the forces required to accelerate then from a stop, reverse their direction, and as I see a spring return, overcome that additional force. Inertia comes into play and I wondered where the top speed would be when the bounce and float would come into play. Also I noticed as the cam came around, a bit of side motion towards the right. Possibly this could be addressed with a hardened wear plate, or even a fixed bearing to control wear and keep better control of the downward force.

Just my preliminary observations.
 

JimDawson

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Thank you Tony.

At that spring rate, about 20 lbs at max compression, the ram tracks the cam pretty well up to about 400 RPM, greater than that, there is some bounce, I have run it up to about 700 RPM and it was still working but a bit noisy. Per the specs, the actual operational speed is 360 RPM, but I did try to design for double that. In actual use, I suspect that it will be operated at < 200 RPM. There is a return spring in the front cover/bearing support that was not installed for the video. It's rate is about double the spring I was using in the test. I just grabbed something out of the spring box for testing. There is also a return spring in the tooling, but I suspect that it's rate will have to be increased. With a 4200 oz-in motor, I'm really just using the brute force method. There is one other small issue, I somehow made an error in the cam design. It was supposed to have a lift of 0.328 and I wound up with 0.480 lift after the third iteration. I didn't catch it before I built it, I don't know how I missed that one. The customer wanted 0.750 so I guess that's a compromise.

I also have some concerns about the lateral motion. Ideally the ram should ride in bearings, or actual ways. The design challenge was not having enough meat in that area to install bearings. When the customer specifies a HF arbor press, and won't budge off of that, well, he gets what he gets. I suspect that the service life of this one is not more than a couple of months. In terms of the number of strokes, this will see more use in an hour, than the average arbor press would see in a lifetime.

I have a new press frame designed that the power head will bolt right into when this frame goes south.
 

randyc

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I didn't even think of "valve floating" (just an example of the problem that Tony mentioned,) ! Are you using an angled roller follower ? I can't WAIT to see that thing running :)

PS: Weird that your customer specified the lift of the cam. It seems obvious that the material is either soft or thin. Less lift = more mechanical advantage and less wear.
 
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randyc

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JimDawson

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I still don't get the high cam lift though, wonder why ... :)
I developed 3 different cam profiles, and I suspect on the last one that when I drew the circle for the max diameter, I typed in the wrong value and just didn't catch it. It works, but is not exactly what I wanted.
 

randyc

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I developed 3 different cam profiles, and I suspect on the last one that when I drew drew the circle for the max diameter, I typed in the wrong value and just didn't catch it. It works, but is not exactly what I wanted.
Sure, but why did the customer specify the lift, that still sounds strange to me ? (Ignore if this is proprietary.)
 

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The customer wanted 0.750 lift. I felt that was too much after I did the torque calculations, so I told him he could have 0.312, but after generating the first profile, it actually came out at 0.328. I think it will be OK at 0.480. I'll know in a couple of days.
 
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Very nice! Are you building the bottom die as well? I apologize if I may have missed that question in this thread.
 

JimDawson

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Very nice! Are you building the bottom die as well? I apologize if I may have missed that question in this thread.
Thank you Andre.

No, the die already exists. I do want to build a new one for the customer and clean up some of the design in the existing one. That will be a whole new project and unfortunately I won't be able to post that one.
 

JimDawson

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A bit more progress on the press.

In the last progress post I completed the cam except for the keyway and the set screws.

My wood splitter/keyway press. I didn’t have a 6mm broach, so I used a 3/16 and will step the key. I had to key from both sides because the broach guide is not long enough to do it in one shot.

IMG_0649.jpg

Using the same mandrel that I made for doing the lathe work, I put it in the mill and cut a 3/16 keyway in it. That way I can clock the cam to drill & tap the setscrew holes over the key. The mandrel end is supported by my patented clamp kit screw jack.

IMG_0651.jpg

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Stepping the key. I needed a about 0.060 more height, so a 1/16 drill bit was a perfect solution

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Installed on the motor, looks like everything lines up.

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Drilling the ram for a ¾-16 bolt.

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The height adjusting bolt installed.

IMG_0661.jpg

I had to drill & tap the motor shaft ¼-20 to install the limit switch cam. The motor was too tall to sit on the table to drill the shaft, so……. A little creative setup. I just hung the motor off the back of the table clamped to an angle plate. I had to pull the way cover back to use the ways to align the motor base. I don’t know what the motor shaft is made of. It isn’t hard, but it worked hardened if you looked at it wrong, much like machining D-2. I couldn’t get through it with a cobalt drill so I wound up using a carbide drill bit to get through it, turning at about 200 RPM. It tapped just fine. Very strange material, might be a stainless alloy. I should note here that I normally would not allow a rag anywhere around spinning tools, but in this case I needed to prevent chips from falling into the motor bearing, and to protect the motor shaft from the vice grips.

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The LS cam installed. This activates the Stop-On-Top function.

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The electronics. On the left is the stepper drive. This one is kind of interesting in that is has it’s own built in power supply. It takes 115/230 volts AC in. On the right is the 12 VDC power supply for the stepper variable speed module (top right). The stepper drive is mounted with screws; the other two devices are RTV silicone glued in.

IMG_0017.jpg

The operator panel. On left is the speed pot, For/Rev switch in case of a hard jam, E-Stop, and Run button. The speed pot is calibrated so that 50 = 5 strokes/ sec. I kinda messed up and ordered the wrong box, not deep enough so I should have the new one in a day or so.

IMG_0022.jpg
 
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