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Thread: Die alignment: To dowel the punch holder or the die holder first?

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    Default Die alignment: To dowel the punch holder or the die holder first?

    I have made a few progressive dies now, and have been struggling with finding the best technique for aligning the punch holder block and the die holder block within the die shoe.

    My technique is to fully dowel and screw one of the two (punch holder or die holder) in place, and the other one is only held by screws but no dowels. This way, once assembled, I can adjust the precise location of one of the two blocks to get the punches and dies to mate properly. Once in place, then I lock down the screws, drill through the block and die shoe and dowel the part in place.

    Now here's the dilemma: Since the die shoe has slug holes in it which need to match up with the die buttons in the die holder (and I'd prefer not to make the slug holes oversized), it would seem preferable to dowel the die holder first, and let the punch holder float for the adjustment. However, since the punch holder has punches sticking out (which are long), I would need extra-long drills (which are less accurate) to clear the punches when I am ready to dowel the punch holder, and sometimes there just isn't enough clearance for the toolholder to drill dowel holes which may be close to the punches.

    So because of this, I have to dowel the punch holder first, and let the die holder float for adjustment, since there are no tall protrusions on the die holder. But like I said, I would prefer if I could do it the other way around...

    I'd like to get some of your input on how you get around this issue, or what order you do these things, or I'd like to know if you have a totally different way of handling the alignment.

    Thanks!

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    There's several different techniques to use and I'm not the last word on this either. May I begin by asking why the punches are so very long? Any good design will use as short a punch as possible to avoid the potential misalignment over a longer length. Even if your part has large "Z" depths to it a shorter punch can be mounted (where possible) on a block to make up the difference in Z. I've only had the occasional punch exceed 3-4 inches in length. Any punch longer than 6" is a candidate for examining the die design.

    Most dies I've built I pinned the punch plate last. Transfer screws, 1/64 under dowel size drills, and careful checking of clearance alignment between every operation is critical. How you ensure the alignment of punch to die section is also quite important IMO.

    How long are your punches that a standard drill length won't reach? There are smaller drill chucks, I've also made drill/tool holders for extra reach. If you've spotted the location of a punch plate/holder then you don't need to leave it mounted to perform the full depth of the hole. Once you established the hole location (3-4 times the hole diameter for example) then leaving the punch in place to do the rest of the drilling/reaming/tapping runs the risk of damage occuring. I always just spotted the location, removed the punch, and then finished the operation. Initial reaming of dowel holes was done with an undersize reamer with the punch plate mounted and then final size (.0005) with it removed to avoid changing the reamer size (hardened punch holder) or the hole size (soft plate).

    The above is for dies with .003+ clearance per side, less than that and the % of misalignment begins to greatly affect the results. For those sort of clearances a radial drill press can be used for lots of the hole work. For clearances of less than .002 per side there should be other machine/assembly methods to ensure accurate locations. Even the die components will change per the tolerances of the operation (box stripper vs. spring type for example)

    My point here is that every die has it's own requirements that dictate the machines used, the assembly methods, and alignment procedures. I'm not trying to be vague here, just noting that every job is somewhat unique. More info about your work, material, die design, etc. will probably net more info from the crowd.



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    Hi RoninB4, thanks for your reply. I've attached a drawing of the punch holder / punches / upper die shoe from a current project for your reference. This one is a simple perforate and pilot die. The two dowel holes which would be drilled through to the die shoe after alignment are the holes in the extreme upper left and extreme lower right on the punch holder block.

    So it turns out that for this particular die, I do have sufficient clearance away from the punches to drill the dowel holes with the punches installed (allowing the punch holder to be doweled after the die holder).

    However, on other dies which I have worked on in the past, due to space constraints, the dowel pin locations were located much closer to the punches such that the drill toolholder would interfere with the punches, making this approach difficult.

    That's interesting to hear that you have used special long holders (and even made your own) to clear protrusions at times.

    My punches are not especially long - they're only 2" long (with the pilots being a little longer) which is around as short as they come, not including the extra stubby ones used in special situations.

    So given a situation where the dowel pin locations are closer to a punch than the radius of the toolholder, even with short 2" punches, you'd need a really long drill to clear everything (for example, 2" punch height + 1.5" die shoe height = 3.5" worth of drill sticking out of the toolholder. I'm generally using 3/8 dowels, so for a drill bit that's less than 3/8", that would require an unusually long drill. Your suggestion to just get the drill through sufficiently far into the die shoe to establish location and to finish the hole later with the punch holder removed is good advice which I am sure I will use in the future.

    In writing this, I realize that one thing I can do going forward is to design my dies such that the dowel holes are sufficiently far from any protrusions... But sometimes that isn't an option where there are space constraints.

    This may be getting off topic slightly, but you mentioned the use of other alignment methods when a design calls for very tight clearances. On one of my first dies, I was working with 10% total clearance on .024" material (0.0012" clearance per side). I was having issues with punch tip breakage because my alignment was not perfect and the punches were having to force their way into the die buttons instead of sliding right in. What sort of special techniques or machines would you use given the requirement of very tight tolerances?

    Attached Thumbnails Attached Thumbnails -upper-die-shoe-punch-holder-pdf  


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    Progressive die especially when made in sections - die holder first. Should be no problem to mount the punch holder.



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    Quote Originally Posted by PhoenixMetal View Post

    My punches are not especially long - they're only 2" long (with the pilots being a little longer) which is around as short as they come, not including the extra stubby ones used in special situations.

    So given a situation where the dowel pin locations are closer to a punch than the radius of the toolholder, even with short 2" punches, you'd need a really long drill to clear everything (for example, 2" punch height + 1.5" die shoe height = 3.5" worth of drill sticking out of the toolholder. I'm generally using 3/8 dowels, so for a drill bit that's less than 3/8", that would require an unusually long drill. Your suggestion to just get the drill through sufficiently far into the die shoe to establish location and to finish the hole later with the punch holder removed is good advice which I am sure I will use in the future.


    This may be getting off topic slightly, but you mentioned the use of other alignment methods when a design calls for very tight clearances. On one of my first dies, I was working with 10% total clearance on .024" material (0.0012" clearance per side). I was having issues with punch tip breakage because my alignment was not perfect and the punches were having to force their way into the die buttons instead of sliding right in. What sort of special techniques or machines would you use given the requirement of very tight tolerances?

    -Well I guess your punches aren't really as long as I had imagined by your first post, they're really about standard length. As for the 2" punch and 1.5 die shoe I would have to ask one question first. Why would you think you need drill all the way through with everything mounted? Spot it, remove the fragile bits and have a go at the spotted location with an undersize drill. Drill all the way through, flip the shoe and drill oversize (clearance) and/or c'bore for back mounting screws. You don't need the entire 1.5 thickness of the shoe to be reamed, you aren't getting more location after 1.5-2 X the dowel diameter so clearance the rest. This would presume you have already drilled for mounting the punch. If not, then line up the punch/plate in the appropriate manner and use transfer screws for the SHCS locations. Then do the dowels w/the undersize drill. Remount the punch/plate and line up the die clearance. Lock down the punch/plat, ream undersize, remove the punch and ream full size for the dowel. So you'll need to have 2" plus 2xD of dowel. Most reamers over 1/8 should be plenty long enough to clear tooling height.

    As for the "other methods", you would need to estimate the die requirements. Accuracy, cutting clearance, available machinery, and expected life of the die all come into play. For close work, thin material, short press stroke I like to use a box stripper design. It's more costly to produce but pays off in accuracy/punch life. Press condition also makes a difference. If the press is sloppy then you'll fight way wear with a wandering ram. Spring strippers are just fine for relativelty thicker material. Spring strippers are also good for form work that incorporates traveling pads and side cams. An added bonus of spring strippers is the use of transfer pins and loading the springs according to spring type AND locating them where they're needed most. You're loading by location where the stripper needs the pressure to hold the material.

    There's certainly more than one way to skin a cat, these are just some of the methods I've used that worked well for the application. How long have you been working on progressive stamping dies and where did you learn this?



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    For really close work we don't even mount the punches to the upper shoe.

    All the components are mounted in a self-contained "mini-set" that mounts to the lower shoe.

    Opening and stripping are accomplished with the spring stripper and auxiliary springs.

    All the components are cut in our wire-edms.

    Use the same method to punch everything from .001" FH 301SS to .075" 1018CR.

    I cannot remember the last time we had an alignment problem between our punches and dies doing this.

    For heavier work where we have to mount to both shoes we use what works best for that die.



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    I always do the punch holder last, when setting a die by hand. For the reasons stated above for slug clearance holes.

    And also like mentioned, havent had too many instances where I couldnt get a drill/reamer to the hole. may have had to make that special quick, adapter but it works.



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