Making some 3" shrink dies for a friend with a Yoder K 90 M and some radius dies for a friend with a Pettingell #2. I first squared and machined the blocks to the correct dimensions for the large 3" dies, then cut the 10 degree dovetails that hold them in the hammer. I then had to build a new fixture to hold the 3" material in the rotary table to cut the thumbnail ramp. I made this one larger and heaver...there is quite a bit of stress on the die during machining and I didn't want it to move so I can hold tolerances.
To cut the cove in the top die I had to make a fixture to hold the die at a 15.5 degree angle on the rotary table so that I could cut the cove with a 7/8" radius, 1.5" wide and 1.5" long.
Cutting the 10 degree dovetails in the Bridgeport mill.
I made dies that mount both perpendicular and parallel to the dovetail in the hammer anvil. This allows me to stretch the shape on large panels without having to feed the panel from an odd angle. The picture on the right shows the die installed in the Powell Hammer. A radius top die is used with a small flat area in conjunction with the stretch die on the bottom rather than the normal flat top die.
Received the dies back from the vacuum heat treatment process. The photo on the left is of the dies just as I received them after vacuum heat treatment. They don't have any scale, just a little dull finish. The photo in the center is a set of dies i had heat treated earlier with the conventional open furnace...the scale that forms during the process must be removed before they can be polished. The photo on the right is the vacuum treated dies after a quick buff. They are now ready to be sent off to the Roadster Shop.
Making some 3" radius dies for a friend with a Pettingell #2. A 36" radius bottom die in progress shown here. Rather than chucking the die blanks up in the lathe 4 jaw chuck and cutting the radius or grinding the radius on the belt grinder, I cut the radius on the manual Bridgeport mill using a boring bar. The technique is discussed in the Tom Lipton's book referenced earlier on squaring the blocks. The first 2 pictures show the set up in the mill, the third picture shows the rough cut radius and the 4th picture show the radius gage on the block. The mill cuts the radius very accurately using this technique...it's quick and easy. I'll also relieve the corners with this technique next.
Views of all sides of the dies. They are now ready for heat treatment to hardness 56 on the Rockwell C scale. After the heat treatment they will be cleaned and polished then put in the Yoder side of the Powell hammer.
Making Linear Stretch Dies
The flat top die and the 24 bottom dies are for a friend who asked me to make them for him.
Before I start forming the dies, the blocks must be milled square, and parallel. There is a great discussion on how to mill blocks square in Tom Lipton's book. You may know Tom from his Oxtools videos. Once I get the blocks square and parallel, then I can start milling them to the required dimensions.
You can use the Spherical Segment used in the Kurt mill vise instead of a ball bearing to hold the block against the fixed jaw of the mill vise. They are only $4.00 on the Kurt web site.
Here is the lower die roughed out with the thumbnail ramp and the radius sides shaped. Shaping the die is much like sculpting tool steel with a file. It is time consuming and laborious. The next step is to shape the upper die, then polish and tune them in a hammer followed by heat treatment.
Here are the dies after cleaning them up and polishing the hammer surface. They are now hard and ready to be used.
Machining Dies for the Powell Hammer
The first die is squared. Tom's process works...the blocks are square and parallel and it doesn't take much time or trouble.
I cut the cove on the front and sides and cut a radius on the edges. Now the file work by hand starts.
Just received another shipment of S7 steel blocks. Will make some 3 inch dies for Yoder K 90 M and Pettingell #2 hammers.
Fit check at Steve Powell's shop
The rough-cut die ready for fit check
After the dies were made to specifications, they were run in the Powell Hammer. They shrank the material well but left unwanted tool marks in the material. The final process is to tune the dies in the hammer to eliminate the marking. I coated the dies with Dykem and ran them in the hammer. The Dykem shows how the surfaces are mating. I marked the dies in the left photo to show the areas where I will grind away material based on the markings. I did this several times until I obtained the desired results. The final configuration is shown in the photo at the right. Everyone focuses on the male bottom die when it is actually the upper female die where the magic happens. Most of the tuning work was done on the top die.
I cut some brass pellets to put in the holes with the hold-down screws to prevent them from distorting the work. The fixture is shown here on the rotary table on the Bridgeport mill during machining the male die. The fixture holds the work well without any movement or instability.
A special thanks to Jim Hervatin (Kustoms by Jimmy) and Ed Thomas (Thomas Restoration) for their help and wealth of experience. Jim opened his shop and allow me to use his big Yoder...Ed and Jim both worked with the dies to improve their performance. There is no substitute for experience, friendship and a willingness to help others. Their help and friendship is greatly appreciated.
First 2 dies ready for heat treatment. A 24" radius bottom die and a flat, top die. Will be hardened to Rockwell number 56 on the C scale.
Churning out 2 1/4" dies...next comes shaping the radius for each of the different value dies.
Making 3"Linear Stretch Dies
I am making a set of 3" linear stretch dies for a friend with a large Yoder. I added a surface grinder to the shop to grind the blocks flat and parallel. Milling the blocks with a shell mill and carbide inserts left marks in the blocks, and while the surface finish was good, it was not as flat as I would like. The surface grinder makes the process take longer and requires more work per block, but the blocks are more accurate and have a much better surface to form the desired die with. The picture showing all 4 block on the grinder is just for photo purposes...the blocks were ground one at a time.
This is the material for the 2 1/4" dies used in the Powell Hammer and in LK 90 M Yoder hammers. This shows the raw S7 tool steel blocks as received. S7 is also trade named Bearcat.
Here are some pictures of the male die after the rough machining process. Next will be machining the sides and hand filing and shaping of the thumbnail ramp.
The top left picture shows the die after relieving the sharp corners. I then put together a spinner to hold the die centered while allowing it to rotate so that it can be smoothed, or blended, on the belt sander and polished. The rotation of the die, or spinning, allows you to maintain symmetry across the radius and the corners while smoothing the die. I used an aluminum block that I machined with 10 degree dovetails to hold the die on the shaft of the spinner to reduce weight. The S7 steel blocks are heavy and adding a steel holding fixture would add more weight so I used a lighter material and put end blocks on the fixture to clamp and secure the die rather than pinch screws in the side for added strength. The second photo shows all the parts of the spinner before assembly. The top right photo shows the die mounted in the holding fixture before I installed the end clamp block. The bottom photo is the die and the spinner as I used it on the belt sander and the right photo is the final product after polishing. Now ready for heat treatment.
Here are all the 2.250" linear stretch dies I made for my Powell Hammer; a 90 degree die, a broad faced die, a narrow faced die, a top die and a 1.5" top die.
These 2 pictures show the thumbnail ramp after hand filing into shape. I used a radius gage while forming the ramp to keep the curve accurate. This also shows the markings for the cove in the front and 2 sides of the die. All the work was done on a manual mill and with had files. I find filing easier to control than using grinders. The coved sides allow the material being shrunk to move in and out of the hammer without being marked by the sides and front of the die.
This is a 1.5" top die to be used with the stretch dies to pre-stretch areas that will be beaded.
First 2 dies back from heat treatment. This is what they look like if the heat treatment is not done in a vacuum furnace...there is a scale coating that must be removed before polishing. Vacuum furnace heat treatment turns the material a straw yellow without the scale.
Got a little time in the shop this past week away from the house renovation and cranked out some more dies. A 36 and a 12 bottom die plus another flat top die and another 24 bottom die. Will work on the shrink dies next, then take the batch for heat treatment.
I assembled the fixture around the male die and clamped it. Then TIG welded the pieces together. The fixture is now ready to mount on the rotary table and the die is secured with two 1/4 inch cap screws.
Made a set of 3" dies that are the big brother to the 2 1/4" set I made for my Powell Hammer. The big dies are used in the Pettingell #2 and the Yoder K-90M while the small dies are used in the Yoder LK-90 and the Pettingell #1. I used the surface grinder to form the final size of the basic blocks, to make them flat, square, parallel and on spec dimensions. It takes a little longer but makes the blocks a lot more accurate and makes it easer to form the dies.
To allow more aggressive filing I made a mask from some thin stainless steel that I had left over from the wife's kitchen remodel. I learned to do this from the firs shrink dies I made to avoid file marks on the floor of the die. I first made a paper pattern and then used it to cut the stainless steel mask. The die is shown at the right with the mask installed in the vise during shaping of the thumbnail ramp.
Surface Grinding the Blocks
The photo on the left shows the lower die roughed out and the upper die as it came out of the Bridgeport mill. The middle photo shows both dies rough finished and ready to put into a Yoder K 90 M hammer for tuning so that they shrink metal and do not leave tool marks in the work. The photo on the right is after running on the Yoder K-90 and tuning. Now they will be heat treated followed by polishing. I'm using a vacuum heat treat process with these dies.
I decided that it is easier, quicker, and cheeper to rough cut the dovetails with the band saw first, then use the milling machine with the expensive end mills to finish them. Worked out well and was much faster...also less wear on the end mills.
The linear stretch die stretches the metal generally in one direction rather than in all directions as the radius dies do. The linear stretch dies are used in making reverse curve shapes and stretching over shrunk areas. The dark oval area on top of the die is generally flat with a radius blended off the edge from the oval. The long, slender flat tends to stretch the metal toward the long part of the oval.
I finally got some time away from the home renovation again and started work on the 2 1/4 inch shrink dies for my Powell Hammer. I machined some 1/2 inch mild steel for the fixture to hold the male die in the rotary table for milling the thumbnail. I cut the two side pieces and milled the 10 degree bevel on both sides to hold the dovetail in the die.
This picture shows the dies after the machining and filing are finished and cleaned up. One of the changes to the process I will make when machining the next set of shrink dies is to make a mask for the floor of the male die to protect it while filing the thumbnail ramp. I allowed the file to hit the ramp floor a few times and left file marks which will not affect their function but just don't look good.
Cut die blanks for the thumbnail shrink dies. Now comes the hard part...shaping the dies.
The surface grinder makes a lot of grinding dust and mine didn't come with a dust fence at the end of the table. So, I decided that I'm supposed to be a metal shaper and should shape a fence. I had a pice of 18 gage steel scrap that looked about the right size and I hammer out a fence and put a vacuum connection in it. I need to paint it now to prevent rust, but this is my solution to the grinder dust problem. We'll see how it works.
I mounted the hold-down fixture on the rotary table and centered them on the Bridgeport mill. I laid out the pattern for the thumbnail on the die block with Dyekm and scribed the dimensions. I mounted the die in the fixture and centered the thumbnail radius. It was then just a matter of machining the die...the set up is the time consuming task.
Copyright © Jack Pledger