TECH - Building a Pullmax-Style Hammer

Here is my entry for Tech Week. Tech articles are the coolest and I wish there were more of them on the HAMB!!

I decided to build a Pullmax-style reciprocating machine for three main reasons. 1) I’m too cheap to cough up the $6k needed to buy a new one 2) I’ve got my mind made up that my next hot rod I’m going to build from scratch and 3) the Pullmax-style hammer is a very proven and versatile design. My design incorporated 0.750” (19mm) tool holder shafts which makes it compatible with all commercially available Pullmax tooling. I don’t think that you could (easily) build a power hammer without access to a machine shop.

I’ll include a complete BOM and drawings at the end of this thread. Since most of the material used is pretty short you could probably pickup some drops pretty cheaply from your local steel yard or machine shop. The total cost for my build is $400 because I had almost all the material lying around.

NOTE: Most of my inspiration and some of the design came from the guys at the www.metalmeet.com and http://allmetalshaping.com forums. If you have not checked out those sites you should. The stuff that those guys can create with metal is pretty amazing.

This is not a tutorial in how to use a mill and lathe. If you have a mill and a lathe I assume you know how to operate them!!

Step 1: Upper tool holder slide
This is the business end of the hammer as most of the assembly is stationary. This was made from a billet piece of aluminum that I had lying around. This could be made from steel, but aluminum is much easier to bore and this piece does not really see any force as the hammer shaft should always “float” between the bearings because the stroke is limited by the offset in the driveshaft. The orientation of the upper and lower dies is critical if you are running shrinking dies. If you have any mis-alignment during the hammering you will get marks in the piece you are shrinking. In theory the connecting link will keep the shaft oriented correctly, but I wanted to make sure there was not any deflection or movement. I came up with a slotted design that uses roller bearings to keep everything oriented. The roller bearings are cheap and easy to replace when they wear out. I used commercially available bushings for the shaft to ride on because they are cheap and easily replaced when they wear out.

The upper tool holder slide must be bored for the bushings. A slight press fit will do the trick.


Holes are drilled and tapped into the block. A slot is milled on each side for the needle roller bearings to ride in. This will keep the upper tool holder oriented during operations.


Machining completed with bushings installed



Step 2: Upper tool holder
The design of the upper tool holder has to address the tricky square-in-a-round-hole problem. It is slightly more complicated than the lower tool holder because the shaft has to move up and down. I “cheated” on this design and purchased a square collet from Reid Supply. This was built from a 7.5” long piece of 4130 material I had from another project. The square collet was welded into the upper tool holder to ensure perfect alignment once everything was assembled. The tool post bottoms out against the bottom of the bore so they weld does not carry any load – it just orients everything correctly until the clamp is applied. The clamp was made from a shaft collar. The shaft collar was secured to the upper tool holder and then the holes were drilled and tapped through. In theory I could have made the upper tool holder out of a large OD piece of material instead of using the shaft collar, but I’m too lazy to turn down the OD that much. The machining of this was fairly easy because I have an indexing vise, but it could be done with a standard vise if you lay everything out properly.

The shaft OD is turned and polished on a lathe.


The slot for the connecting rod is milled out.


Hole is drilled for the connecting rod bolt and flats are milled. The flats are only for the bolt and nut to shoulder against.


Holes are drilled and tapped into the shaft collar. These set screw will provide the clamping force on the square collet.


Machining complete


Completed assembly showing the needle roller bearings. The design uses two bearings – one for the upper tool holder slide and one for the frame. The shows the collet after it was welded in. The weld does not carry any load – all the hammer load is transferred to the bottom of the bore.



Step 3: Lower tool holder
This is my version of the design that “TheRodDoc” posted on the metalmeet.com forum. His design greatly simplified the square-in-a-round-hole problem and was easily built with material I had lying around. I did not have a chunk of steel this big so this was made out of multiple pieces of flat bar. They are pinned/welded together and them all squared up in the mill. Once the cover plate is bolted on nothing can move. This must be made of out of steel because it carries a considerable amount of load.

Flat bar welded together and squared in the mill.


Drilling and tapping the holes


Machining completed with tool shaft installed. The height of the side was milled down so the cover plate can clamp tightly against the tool shaft.


Cover plate


Bottom plate which will be welded in place


Completed assembly


Completed assembly with adjustment screw installed. Since I don’t have a 3/4" – 6 stub acme tap I just welded a nut. The welding was done with the cover plate installed to make sure everything stayed lined up.


Step 4: The frame
I had originally planned to have the frame waterjet from 1” steel. This could have left a clean edge and eliminated any heat affected zone. I got three quotes and they were all around $450-500 per plate so I decided to use some 3/4" x 4” flat bar that I had lying around. If my frame did not work I would spend the money. I can send you .dxf version of the frame if you want to get it cut out. The only thing that is super critical on the frame is the alignment of the top and bottom tool holders. It could easily be made from square or rectangular stock.

The same bolt pattern and slots were machined into the top arm. The needle bearings can easily be changed out without taking the head apart if needed.




Step 5: Assembling the frame
Once everything is bolted together a piece of key stock was inserted into the tool holders and then the square collet in the top tool holder was welded in place. This assured perfect alignment between the two tool holders.

I waited to box/weld the frame together to make sure the alignment was perfect.

 

Step 6: Driveshaft
I decided to use a 1/8” offset in the shaft which will give the power hammer a 1/4" stroke. I thought about making the stroke adjustable, but I can always do that later if it does not work like I want it to. I don’t have a 4-jaw independent chuck on my lathe so I had to get creative to get the offset into the shaft. This shaft carries all the load of the hammer so it cannot be made from mild steel. The pillow block bearing on the front of the hammer must be mounted as closely as possible to reduce the shaft deflection (not like the picture above...).

I bored a bushing with a 1/8” offset that would slide over the shaft. This was then slotted so it could be clamped onto the shaft.


Here is the finished shaft (yes, I know it is a bad picture). Since this involved a lot of interrupted cuts the feet rate on the lathe was very slow. I used a hardened staft that will hopefully hold up to the constant pounding.


Step 7: Connecting link
The connecting link ties the driveshaft to the upper tool holder. I used a bearing on the top end and a bushing on the lower end. I’m not sure if the bushing will last, but I can always make a new one and install a bearing if needed. After a few hours of use it shows minimal wear. I was too lazy to machine rounds on the edges.


Step 8: Mounting the motor
Now that everything is assembled the motor needs to be mounted. Since the motor frame has slots in it I did not see the need for an idler pulley. I’m running a 1 hp motor with a 4 to 1 reduction for around 850 beats per minute. I need to add a foot switch into the on/off loop for easier control.

Step 9: Mounting the base
Now that everything is assembled you have to decide what to mount it to. You could easily mount it to workbench, but I scavenged up a baseplate that worked perfectly. I added some wheels to make it mobile. It is at chest height which makes it very easy to see what you are working on.

Step 10: Making thumbnail dies
My original plan was to purchase a set of thumbnail dies, but I decided that before I spend hundreds of dollars I would try to make a set of my own. Since my are not hardened they will not last forever. I did not make a drawing for these since I really did not know what I was doing. If you hammer on some aluminum it is pretty easy to see where you need to take more material off.

Two pieces of flat bar were squared and then welded together. A hole was drilled through the middle at 18 degrees.


The tool holder posts were squared off in the mill.


The tool holder posts were installed and the dies put into place. They were welded in place and then cut apart to ensure perfect alignment.


Here are the dies opened up. I welded a 1/2" bolt and relieved the recessed die.


These dies shrink the metal by creating a "thumbnail" in the metal and then compressing this indentation into itself as the sheetmetal is pulled back out of the machine. The more you shrink a piece the thicker the metal will get. Here is a picture before the metal was pulled back through the die.

 

bad ass...

 

As promised here are the drawings and BOM. I'm not sure they are 100% accurate, but they should be pretty damn close. I was kind of creating drawings as I machined everything. I did this for fun, so don't get all mad if something is wrong or not dimensioned correctly!! If you try to sell my drawings and/or use them to make money you are a little bitch.

Once you get the upper and lower toolholders made you can really make the frame look like whatever you want. The throat on my machine is 8" tall x 24" deep which will allow me to make 48" wide panels.

So far it works well. I have not made anything other than a couple of bowls because I all I had was small pieces of sheetmetal lying around. The next thing I need to make for it is a set of planishing dies. It will shrink up to 16 gauge metal, but is much happier with 18 or smalller.

-Drew

 

got my vote... friggin hard core man. nice work indeed

 

awsome!

 

really nice work man. I cant seem to stray from my projects to build anything like this yet.

 

Nice job, and the drawings are nicely done - Thanks for sharing them!

 

This is the best Tech i've seen in a long time.......endless possiblities.

 

Thanks everyone for the kind words.

This was built more out of necessity than anything else. My wife bet me $1000 at the roundup this year that I could not make it 1 year without buying another vehicle. She never said anything about building one from scratch!! My plan is to try and build a roadster.

 

That is great stuff, love this kind of deal, keep up the great work!

 

Your fab work is first rate but I paid $1400.00 for my P5 Pullmax out of Millwaukee only to find a P3 7 miles away for $800.00 a year or so later. They are out there for reasonable money.

 

WOW what a great post. Put this one into the memory banks.

 

WOW!!!!! Very awesome!!!!

(note to self: buy machining tools so I can build this)

 

WOW! Awesome.

 

my vote also

 

nice clean work i want one

 

This is too friggin' cool! Going to have to read it again so it really soaks in. Awesome work.

 

Hell Yeah!!!!!!!!!!!!!!! Great tech writeup I always wanted a P5 Pullmax, but could never afford one. Now if only I had a milling machine

 

You sir, are a badass! Great tech! Would love to see a video of this thing in action!

 

Freakin awesome

 

poofus i will be building something similar to this in the next couple months, if you want to make one as well let me know.

 

No need. I built my first one back in 2004 with nothing more "machine tool"-like than a chop saw and a drill press. As you know, there's more than one way to skin a cat! It wasn't quite as pretty as Drew's, but it was enough that someone decided they needed it more than I did

Nice work and nice write up, Drew!!

Tim D.

 

you rule

 

how thick of materal will it do?

 

Kick ass! I need one of these. My boss just gave me a mill and lathe, and I was just thinking what else I could make with them. Thanks for putting this tech together!

 

one of the best Tech's on Hamb - Excellent

 

Good job!

 

Agreed - I've seen some very nice hammers built with nothing more than a welder, drill press, and chop saw.

 

re-read it... he said 16, but its happier with 18 or less