Servo Punch Press

[JimDawson]

OK in the previous post one side of the connecting rod was finished, so now is time to do the other side. So first mill a con rod shaped pocket into the aluminum. 0.125 deep and a loose press fit. This locates the part exactly back relative to 0,0 without having to dial anything in after it's turned over. The screwdriver pockets are so it's possible to get the part out of the aluminum block, you need to pry it out.



The same operations were performed on this side as the first side. I left the ''island'' on the crank end because I didn't have enough meat in there to counter bore for a screw. So I used flat head screws on this side for tool clearance.

Also you now see why the side screw holes were there. All they have to do is hold the part down, the pocket holds it in location. The next step is to pocket and bore the bearing and pin holes.


While the con rod was running, I was setting up to fab up the feed rollers in the lathe.
12 x 4 inch dia 8620. This was another bit of a screw up on my part, originally I designed the rollers to be 3.800 dia, and ordered the material. After a design review I decided to make the feed rollers 2.75 diameter so I'll be making a lot of chips to get this down to size.

Does this look like too much stick out?


Yeah, I guess it is. Note: The chuck jaws are at the absolute limit of extension where I will run them. So support it in the steady rest to face and center drill. For center drilling I normally face a small area, in this case about 1 inch dia. Then center drill and then finish the face after the center is in place.

 

[JimDawson]

Finishing the connecting rod

First I profiled the big end bore to remove the material as efficiently as possible without having to turn the entire volume into chips.



Then I drilled the pin end with a 1 inch drill then to out a bit more by profiling the bore. Final diameter is 1.250


Then bore to size. Using a 3/4 inch 2 flute endmill for a boring bar. Nice and stiff and sharp. You just have to get the tip of the set at the correct angle. Works great, I use endmills in the lathe for boring bars also when doing shallow bores.


And the finished rod with the bearings pressed in, bronze flange bearings in the pin end. I reduced the mass of the 8 1/2 x 4 x 1 1/4 raw material by about 65%.

 

[FOMOGO]

That came out great. Thanks for the walk through of all the operations. Mike

 

[JimDawson]

Thank you Mike. It's my pleasure to try to show some tricks & tips.

 

[JimDawson]

The next part of the project is to make the driven feed rolls.

The original design called for 3.800 dia rolls so I ordered a foot of 4'' dia 8620. Well I changed the design so now the feed rolls are 2.625 dia. Had to make a lot of chips. This stuff cuts nice, tough, but didn't give me any problems once I figured out the feed & speed and depth of cut. I could only take 0.050 off of the diameter per pass on my lathe.

First face and center drill for the center. When doing something like this, I just face a small circle around the center, no need to face the whole end, the saw cut was pretty straight. Just need a flat surface to keep the center drill from walking around.

Then turn down to 3'' dia for roughing out.


Then over to the band saw to cut into part sized pieces. Once back in the lathe, do the work on the front end and bore for the shaft. The bore will now become my base surface. The bore and counterbore are concentric, but the OD is subject to the runout in the chuck (about 0.003), that's why to OD is only roughed out at this point. For the finished piece, the bore and the OD must be concentric.


Then flip it around and machine the step on the back. The OD of the step does not have to be perfectly concentric to the bore, it just holds a couple of set screws, chuck tolerance is good enough.


Once I have the part to this point it's ready to key, I didn't get any pictures of that operation. I have a Dumont broach set and a broach press. Here is a picture of the broach press, configured as a mini press brake in this picture. Built from a Chinese wood splitter. Not much of a wood splitter, but makes a great long stroke 7 ton arbor press.



Then over to the mill. This is the shaft that the roll will run on in the machine. First mill the keyway.


Then D & T the set screw holes. I set up the spindex because I wanted one hole over the key, and the other at 90°. The part is located off of the edge of the vice so the spindex only needs to kinda hold the shaft. I just shimmed it to the right height. This is the first time I have used the spindex, I've had it for 25 years Had to clean it up a bit before I could use it. I's been sitting in the back of the bottom shelf of the tool cabinet for a long time.


Then back over to the lathe with the shaft in the collet chuck. If I didn't have an accurate collet chuck I would have either used the 4-jaw or turned a stub arbor in the 3-jaw to have a concentric shaft to mount the part on for finishing. This is the best solution because the roll is mounted on the shaft that it will be running on in the machine, so the best concentricity that I can get. This chuck has about 0.0002 runout (after I reground the bore). Now I can finish the OD.


Once the OD is turned to size then knurl so it grips the material. The two rolls are slightly different sizes, I want to outfeed roll to pull a little faster than the infeed roll. About 0.5% difference in the circumference. This should prevent any tendency for the material to buckle as it feeds through the press.

The shaft tried to walk out of the chuck during this operation, so I moved the tailstock center into position for a little added support. Running at 70 RPM with a slow feed. Using heavy sulfur cutting oil. I start with about 1/2 the knurling roller on the part and feed towards the headstock, then feed until about 1/2 the knurling roller is off the part on the other end. Then stop the chuck, reverse the feed, and run back to the start point. If needed, go a bit deeper and run again. I did these in two passes. Don't retract the knurling rollers from the part until you're happy with the result, it will screw up the pattern. I need to buy some new knurling rollers, these are junk, the center hole is about 0.010 off center. The holder is fine.


And the finished parts

 

[JimDawson]

Next is the real heart of the press, the ram. This press is unique in that the die is integrated into the press rather than being a seperate part as in most presses. This is a single use press so this works out well. This means that there is no margin for error and the tolerance stackup has to be minimized. I have been doing surface grinder quality work on the mill, have been holding +/- 0.0001 on the critical dimensions. The good news is that properly set up, my machine will hold those tolerances.

The first step in the process is to get the fixture block set up, the same chunk of aluminum I used to fixture the connecting rod, I just used the other side.

The nut for the wrist pin nut is the item to be made, 2 inch 1018 shafting. The fixturing holes are already drilled & tapped.


The nut mounting holes done.


Then pocket clearance for the nut so it can be attached to the rear ram plate, this way it can be drilled & tapped in the same setup as the pin hole in the ram plate, this insures that everything is concentric.


Aligning the ram plate on the machine 0,0. I just scribed lines in the proper place to set the 0,0 point, nothing critical here because the piece is oversize at this point.


Then drill and C-sink the mounting holes. Using flathead screws for tool clearance.



I screwed the part down and took a shallow profile cut to get an outline and drilled & tapped the nut mounting holes. Then over to the band saw and cut out the part and attach the nut. Again nothing is critical at this point because the part is just roughed out.



The finished part. The sides, bottom, and pin hole location relative to each other are the critical dimensions. 1 inch shoulder screw.


Then I made an identical plate for the front side without the nut.

Then I made two spacer blocks that will hold the spacing of the two ram plates correctly for further operations. These will be used later to mount the bolster plate.


Now I can drill & tap the holes for the linear bearing blocks and the bottom plate. I used a couple of 1/4 '' flathead screws to hold the assembly together.


The bottom plate, also drilled & tapped for the punch holder. I have been able to drill the dowel pin holes and have everything line up, good repeatability.



And the finished ram assembly.

 

[JimDawson]

Next the punch holder that attaches to the ram.

Still using the same aluminum fixture block, I had it pre-drilled & tapped to accept this part. This is a chunk of 4150, same material as the connecting rod. Clamped a larger chunk to the fixture drilled & c-sink, and drill & ream the dowel pin holes. Then did a shallow profile cut to mark the OD, then cut it out on the bandsaw. Then bolted it back down to the fixture for finishing.



Then drill, straighten, drill & ream the 7 punch holder holes. Straighten? After drilling the pilot holes at about 0.170, I went in with a 0.187 endmill to insure the holes are straight, then drill with a 0.236 drill prior to reaming. Then ream with a 0.2495 reamer to fit the 0.250 punch shanks.


Once the holes are reamed then flip the part over and mill the clearance for the punch heads.


And there it is..... the ram installed in the press. The action is silky smooth, I'm happy with the way it came out. Everything fit as planned.

It's really too bad that all of the really cool work is going to be hidden inside the covers.

 

[JimDawson]

I kind of started this thread in the middle of the project so here are some pictures earlier in the project.

Here is the stand that the press will be installed on. 2x2x1/4 square tube. Took me about a day to fab this up.



The press frame showing the crank housing and motor mounts.


Fitting the feed system and linear bearing rails


The rear view with the motors in place.


The crankshaft, made from 3 inch 4340.


Once the steps are done on the right side then go in and nibble out the the left bearing journal. Just plunge a bit with the tool as you are moving the carriage back & forth a bit while plunging in with the tool bit. The crank journal is left at 2.125 inch to be able to turn the eccentric.


Once the journal is roughed out and tool clearance turned, then go in with the right hand radius tool to finish and put a generous radius in the the corner.



Then setup the steady rest and drill & bore the motor end. This will press directly onto the motor shaft. Got a little hot when I was drilling it.


Once cut off in the band saw, I built a plug to go in the end so I can clamp it in the 4-jaw without squishing the end. The threaded end is so I have something to grab onto to pull the plug back out.


Then set up in the 4-jaw to turn the eccentric. To insure the part is pointing directly at the tailstock, both bearing journals are measured to make sure they are in the same plane. This is done by dialing it in then bumping the part with a dead blow hammer until it's lined up properly. The offset is supposed to be 0.375, but 0.3755 is close enough. Took about a half hour to dial in to this point. The bearing journals are 30mm and the crank journal will be 40mm, that way the the connecting rod will slide over the bearing journal onto the crank journal with 0.010 clearance.



The center drill is on the spindle centerline. looks a little weird


Starting the eccentric

And finishing

And the finished crankshaft. I didn't get a picture of slitting the sleeve that presses onto the motor shaft. The crank bearing is a tight slip fit on the crank journal. It has to find its own center so could not be pressed on. The bearing journals are a light press fit as are the crank housing bearing bores.

 

[JimDawson]

With the ram installed in the press, now I can locate the lower die holder. But first it needs a bolster plate to support the die holder. So first make the bolster plate mounts. Normally you would bolt the bolster plate directly to the press frame, but in this case it's impossible to drill any mount holes in the press frame because of narrow opening. So I need to finish the bolster plate mounts that I used to space the the ram when I was building it.

I needed them spaced 4.0190 apart to make sure the hole pattern is correct to match the press fame spacing and more importantly that the dowel pins are in exactly the right place. No way in this case to put in the dowel pins after bolting in place. So two 123 blocks and a couple of 0.019 feeler gauges makes the 4.0190 spacing I needed. So indicate everything in to make sure the work is square with the vice and locate the edges of the R/H part, and set the 0,0 on the top right corner.


Then drill the holes, ream the dowel pin holes, tap as needed and break the **** tap on the last hole https://www.hobby-machinist.com/threads/yall-aint-gonna-believe-this-one.72951/


So after a small mishap in building the bolster/die holder fixture https://www.hobby-machinist.com/threads/moving-a-hole.72977/#post-612155 the bolster plate is complete.



So now comes the real fun. The die holder needs to be located relative to a punch. So this means locating a point in space. I know where the drawing says it should be, but because of the tolerance stackup there is no guarantee it is where it should be and I need to locate it +/- 0.0005. Everything now is relative to the upper right dowel pin in the picture above, that is 0,0 for the rest of the operations. That point will be 0,0 for the the bolster plate, the die holder, and the stripper plate. In a normal press & die setup the die set would be a completely separate build, but in this case the die is built into the press to reduce the moving mass for high speed operation.

The bolster plate is bolted into position, and the ram is lowered so the punch is touching the plate. Only one punch is installed, that's all that's needed to find the location.


Next measure the punch location in the X & Y axes


Then over to the mill, using a dial indicator and the DRO locate the front and side relative to the dowel pin.

Record the numbers from the DRO on the part with a sharpie Then update the drawing with the new values. This then becomes the base to make the die holder.


The die holder is made from 3/4 inch 4150, and is set up on the fixture plate. The two top dowel pins locate the part during machining, they won't be used for locating the die holder on the bolster plate, not accurate enough. There will be another set of dowel pin holes drilled & reamed once the die holder is aligned in the press and bolted down to the bolster plate. The bolt holes are drilled to 1/4'' standard free fit clearance using a H (0.266) drill. This gives some wiggle room for final alignment of the punches and die before the dowel pins are installed to lock the position.

The small holes are drilled & reamed to accept the die buttons, the large die button hole will be done in the morning. A little tiny die button is sitting next to the hole. Never seen one that small before but because of the lack of room around the large die button I had to go with these.

That surface looks rough, but it's really as smooth as a baby's bottom. If I had used a sharper end mill, the little tool swirls would not be there.


Tomorrow the stripper plate/ punch guide

More later.........

 

[JimDawson]

The die holder, really a pretty simple portion of the system. 7 holes to take the 7 die buttons. The center hole needs to be machined to take a 3/4'' OD die button. The somewhat tricky part is the holes have to be very accurately located and on size to allow a normal press fit of the die buttons. So again using the upper right dowel pin as 0,0, Carefully spot drill, drill, straighten with an end mill, and ream to 0.1875, the die button's OD are 0.1878. Makes a nice snug fit.



Then drill and pocket the center die button. This is one of those holes you have to sneak up on. It can not be oversize, nor too tight. So make a cut, measure, adjust tool offset, cut, measure, adjust tool offset, rinse repeat until done. Target size 0.7503 for a 0.0005 press fit, the die button is 0.7508 OD.


Next is the stripper plate/punch guide. When using spindly little punches it's a good idea to build in a guide for them, and especially in this case where the die is actually part of the press. The purpose of the stripper plate is to strip the material off of the punches as they pull out of the holes. In many cases the stripper plate is spring loaded and built into the upper die half. But in this case the material doesn't need a lot of overhead clearance so this system is the best and allows the punches to be captured by the guide holes. The punches will never pull completely out of the stripper plate.

This is temporarily bolted down until I can counterbore the other 4 mount holes for facing. location at this point is not critical because the material is still about 1/16 oversize. This is the bottom of the stripper plate. It gets a 0.100 deep slot down the center as a material guide, 0.010 wider than the material. The material is about 0.065 thick.


Now flip it over and do the work on the top side, and and finish the OD. Then drill & ream the small punch guide holes, these are 0.002 larger than the punches. Then pocket the guide hole for the large punch. Because the stripper plate and the die holder are both done in the same setup and the stripper plate is doweled to the die holder it's pretty hard to screw up the locations. The 4 mount holes in the center were only used to secure the part during machining, they won't be used for securing the stripper plate. They also allow access to the screws securing the die holder to the bolster plate so that final alignment can be done before dowel pinning everything in place. Thinking ahead and order of operation is important to keep from painting yourself into a corner


And completed


I did make a bit of a tactical error in the design, when I was trying to align the punches and dies I found the press frame was out of square. I thought the 1 inch thick top plate would hold it square, but that's not the case. So I need to build a crossmember that will cover the crankshaft housing and fit tightly between the frame sides, and get bolted and pinned into place. This will also set the spacing on the frame halves so the height adjustment works smoothly, it's a bit tight right now. I just happen to have a piece of 3/4 A36 that will fit in there nicely. The hardware was backset 3/4 inch to allow clearance for the wrist pin (shoulder bolt) head so I could screw the lexan guard directly to the frame.




And all of the punches installed and aligned. This area of the press is completely finger safe, as said above the punches will never pull out of the stripper plate, and the absolute minimum shut height is > than 1 1/4 inch. But it will still have a lexan guard on it. Even without the guard this was designed to have no pinch points.


More later...