Pullmax builds all kinds of sheet metal working machines. They are famous for a long line of shears and formers.
|Recently one of these came into the shop needing some repair
and TLC. The model is an AB which is the smallest Pullmax
I had ever seen. Most are about six to eight feet long, a giant C and are very capable machines. They have a die top and
bottom to form sheet metal, and have been used for decades by automotive and aircraft folks to make body panels. They
also have dies for cutting sheet metal which they do in a shear method, and this cutting process works amazingly well.
|This is a number 5 Pullmax the two racks on the right side
of the machine are dies. This particular unit
has more than a hundred dies total, they are limited only to the imagination. The base of the dies are 3/4" and can
be indexed in their holder in any position. The wrench to install the dies is hanging just to the right of the head.
The number 5 Pullmax is about in the middle to high side. The largest I have seen is the number 9 which is
about sixty percent larger. As you can see this machine is about seven feet long and weighs about four thousand
pounds I would guess.
Close up of a forming die and die head with wrench. This die is used to
put formed grove in a piece
|Pullmax AB, I believe is circa late 40's. I had never seen one this size before. It is about three feet long, powered by a 1/3 hp three phase motor. The frame is cut from a single layer or 3/4" plate steel. The AB is rated for material up to 18 ga, and is really happy with 20 ga. Recently after refit we successfully cut 16 ga stainless without difficulty. The bit size for this machine is 3/8" square instead of 3/4" like the big ones. And it does not have the same die interchangeable head, it is design as a shear only. But I think one could custom make a die if that would be a desire.|
|The head is a toggle bolt design, this is the same for all the Pullmax machines. What this does is allow for a vertical stroke that is weighted so that the hit is not solid, if the material is harder than expected or rate of feed higher than optimal the cutting will not jam but float over the top of the material without cutting, and without breaking a bit. Here the pressure is accomplished by the cylinder weight you see at the top. It is in its up position at the moment, and would be swung clockwise to the down position for cutting. In the up position the bits have a gap for sliding in a piece of sheet metal without cutting. There are no bits installed in this photo.|
|Here is a different angle of the toggle. As you can see
there is a number of sections. Starting from the bottom, this is the
vertical slide that holds the top bit.
Next is the link that ties the fix link on top, to the sliding link on the bottom, this central link is the driven joint.
The top link axis is solid and stationary, but the link itself is on an eccentric, so it moves up when the weight is up and down when the weight is rotated clockwise in the down position.
The large bolt on the bottom slide holds the top bit. This was one of the pieces that had to be replaced. The measured size was .512" diameter with a thread pitch of 13 tpi. This is pretty weird, or 13mm with a pitch of 1.25mm
The bottom is stud that holds the vertical slide has a locking nut on the outside and a threaded collar on the inside. The collar set the tension of the slide. We made a brass washer to go between the two. There was some galling between the slide and the collar and with better lubrication and brass against steel after we polished the surfaces, we think it will operate better. A second washer, this one stepped was installed on the top stud to provide a set clearance for the weight.
The link needed a new bottom bushing. It had worn, probably not been lubricated properly and had turned in the link so that the oil hole was no longer aligned and therefore got zero lubrication even if the operator did put a squirt of oil in the hole. When I first found this problem I drilled a new hole to that the oil would get where it was suppose to. This was a quick fix but the bushing was still worn and every little bit lash in this link detracts from the cutting power of bit. So a new bushing was in order.
I started out with the three jaw chuck but moved to a the four jaw chuck and had to re-center using a centering tool made by Starrett. Pretty handy both for the mill and the lathe. Comes with four different tips. The ID of the bushing was .590" and the OD .748". I wanted a very close fit so I cut the OD at .750" and used an arbor press to install it into the link. The ID was drilled using a 1/2" bit so there was plenty of stock to work with.
A moment about the lathe being used. I always like it when
the author takes a moment to show what equipment they are using to do a
job. It isn't a waste of ink, and if it is, its not much
Below is a 1928 South Bend in beautiful restored condition. Like the
black baked enamel finish and chrome wheels and knobs.
Maybe, if I should be so lucky to live long enough, my 1932 could be restored so nicely.
The plan was to do the final ID cut with the bushing installed so that any change in ID from forcing into the link could be compensated for.
The link was put into the four jaw chuck and centered using the Starrett tool. The tail stock on the South Bend is MT2 taper and all my current tooling is MT3 so we had to resort to using a drill chuck from our drill press to hold a boring bar. I have a boring head that I would normally use for this task, but it also is MT2.
On the plus side, the South Bend's tailstock is very nice and has a great set over capability using a square headed bolt on each side. So setting over the tail stock was easy to do. So we basically set up the tail stock using it as a boring head. With .090" to go we moved ever so carefully, checking with the pin and once it was a couple of thousandths shy we finished up with a dowel wrapped in 600 grit wet/dry emery paper.
Notice the tail stock looks like it was once enameled black.
|Here is an attempt at an action shot.
Note the tool holder with the cutoff blade and a C clamp, like I said this machine is new to the mix and tooling is a little short. It is our duty to do the most with what we have, and sometimes a little duct tape, C clamps and spit can go a long way.
Hope you enjoyed the presentation as much as I had making this