Camjack Knurler

[KBeitz]

A spring like this might work...

 

[AmericanMachinist]

This design seems very smart - thank you for sharing. I'm going to make one. I don't have a 3/4" end mill. I'm contemplating using a drill and figuring it'll be close enough for this purpose.

But I'm also debating buying the endmill and having it... I know the $70 is an investment...

 

[Hawkeye]

If you clamp the two pieces with the 3/4" groove together in the right locations, with a piece of, say, 1/8" or 1/4" scrap in between, the drill bit will likely do a good job. Centre the hole on the scrap.

My knurler is still doing good service. I'm quite pleased with the design. Used it several times in the last couple of weeks.

 

[AmericanMachinist]

Thanks. I'm thinking with a sharp bit and an uninterrupted cut it ought to be precise enough for its role in this tool.

I'm going to be adapting the design very slightly at the tool holder portion to make it work with a T-nut in place of a lantern toolpost.

 

[AmericanMachinist]

Finally getting around to building one of these knurling tools. I am considering how to bolt the base into my T-slots on my lathe (no QC tool post). Alternatively, I am wondering if the forces on the tool are light enough that I can insert the base into my lantern tool post which normally holds a 3/8" wide (1/4" bit) Armstrong tool holder. With the cross slide and compound backed out, I'd still get about 5" arms from the rear arm pivot points to the center of the lathe bed.

Assuming the tool is built accurately, I'd imagine there isn't all that much force on the tool base and by extension on the compound, and in my case the lantern tool post. Is that a reasonable assumption? I may use a 7/16" x 1" piece of steel in my lantern tool post if I'm not way off base here.

Thanks!

 

[AmericanMachinist]

I finished my knurling tool tonight. Thank you for sharing the designs and plans.

Two additional notes:

1) I did this entirely on a grizzly mini-mill (and horizontal bandsaw). So if all you have is a mini-mill, like me, you can do this! Just take your time.

2) I adapted the idea for the QCTP mount to instead slide into a lantern tool post (about 3/8 x 1-1/4"). So far this is working fine, I did one test knurl and then knurled a thumb nut for the knurl itself. So if you have a lantern tool post and no QCTP, you can do this!

Edit: Adding note 3) I believe the original design welded the pivot pin for the cam jack. I could have built didnt want to weld, then grind smooth, etc. So far I've just placed the pin in the slot, and run with it (no fastening). I did apply red loc tite tonight to see if that'll hold the pin - merely for convenience sake. An expoxy like JB weld would surely work. So if you don't have a welder, don't let that step intimate you!

Edit: Adding note 4) Although I did purchase and use a ball end mill to cut the slots for the cam pivot pin, in retrospect I'm not sure this was necessary. I believe with a sufficiently long square end mill, the same technique shared by the original author to create 3/4" radii for clamping nuts, could be used to create these small slots. In the event it saves a tool purchase beyond budget. Perhaps with a solid spacer to avoid an interrupted cut a sharp drill could even be used as Hawkeye stated above.

I did notice the arms tend to pull to the side a bit. I believe someone in the thread mentioned adding support to prevent that. May not be a bad idea. Though my first 2 knurls in steel of unknown alloy look great.

I also noticed the need to hold the arms apart to position them onto the workpiece. Not a big deal. May look into spring options at some point. Just position the knurler arms lightly on the work piece with the lathe off. Seems to work.

Thanks again for sharing the designs and plans!

 

[mickri]

I might make one of these. Still thinking about it. After reviewing everything the cam jack appears to add little if any additional force over just tightening the screw on the top piece. The cam applies force to the top piece at two points. Any force applied by the cam and how that force is divided between the two points is determined by where main screw is placed between the two points. In this case the greater force would be applied at the adjusting screw because it is further away from the main screw. Longer lever arm. So the cam instead of applying greater force at the knurl end is applying the greater force at the other end. I won't bore you with the math. The vector diagram gives you a visual on the force distribution.



Eliminating the cam would simplify making it. The top and bottom pieces would be the same shape. Also moving the main screw further away from the knurl end would increase the force on the knurl.

This is a great design and well worth making.

 

[AmericanMachinist]

I think a benefit of the cam is that you get fine-adjustability given the reduction in travel of the two sides of the cam.

I believe the size of the force vectors backward in your drawing. A point closer to a fulcrum experiences a larger force with less travel. The object far from the fulcrum must travel a multiple of times further, but can apply a much larger force to the object close to the fulcrum.

In effect, you might tighten the jaws of the knurler near the 1/2-20 main screw 20 thousandths by raising the rear of the cam 100 thousandths. But applying 1/5 the constant force to the cam screw.

The alternative being a need to crank on the 1/2-20 screw with a wrench and also finding fine-adjust difficult.

Edit to add: I've only built one of these, with cam, and its my first knurling tool. So I can't say with confidence how difficult it would be to use without the cam, BUT the benefits of the cam seem intuitive, and by the time you build the rest, the cam is just a small part of the build.

 

[mickri]

In my reading of the thread the force was being applied by the 1/2-20 screw. The OP mentioned how easy it was to tighten with just the knurled piece on the 1/2-20 screw. The OP also calls the knurled end of the cam the fulcrum which indicates to me that the 1/2-20 screw is providing the downward force. If you are using the adjustment screw on the cam to add more force then you are correct that a small upward force on the cam adjustment screw would create a larger downward force at the knurl end. It would also create an upward force on the bottom piece.

All of these interactions would create complex force vectors. More than I want to try to calculate. But I still wonder how much you are really gaining with the cam. Maybe someone who has made one of these could try to use it without the cam and just applying force with the 1/2-20 screw to see what happens.

 

[savarin]

All I know is it works great and is easy to apply a touch more pressure if it looks like double tracking.
Most of my knurling is in stainless and this knurler works everytime.
I only used a lathe and drill press to make mine.