Bolt Lug Cams

G

glbreil

Guest
I have gotten a copy of Stuart Ottesons Benchrest Actions and Triggers book.

As I was reading (well looking at the pictures) i noticed that most of the actions reviewed including the Original Panda and the Shilen Actions which are both 2 lug actions appear to have the bolt lug cams cut on the bolt instead of in the action.

I know the newer Kebly made Pandas have the cams in the action and not on the bolt.

What do you think about this and does anyone have any good clear pictures of these actions showing the cams on the bolt lugs?

Thanks Gary
 
My thoughts are of the surface area of the lugs. If you incorporate the cams in the action, the bolt lugs remain full size. Since the action lugs are much wider, they can incorporate the cams yet still allow full lug contact area when closed.
 
I agree with PEI rob. But cutting them inside the action in stead of on the bolt lugs, is more difficoult though.
 
Bolt Cams

The cams in the action instead of on the bolt gives more contact area, and the more the better has always been my thoughts also, however when I saw those pictures I was surprised that the cams were on the bolt and it made me wonder if it was truley better or if it just sounds better.

If the strength of the bolt lug is say double the maximum pressure possible, then is there any return by increasing it?

I have built an action of my own and plan to build more, I went to the trouble to cut the cams in the action, but if there is really no return for this then I may do the next one different or may cut part of the cam on bolt parts.

Does any one really know if it is better or if it just sounds better?

Also does anyone have a good picture of one of the Panda or Shilen bolts with the cams on the bolt lugs?

Gary
 
Hey Gary

Do you have any pics of your action? I also wonder on how you cut the cams? do you have cnc or was it a manual method?

Thanks
KB
 
Cam Cutter

KB, I have done a lot of searching and reading about methods to do this, I looked at all of them and think that the tool designed by JayIdaho is probably the best, but in the end I went with simple.

I made a mandrel to fit the action and cut a slot on the ange I wanted the cams and then I cut a piece of file the shape of the bolt lug and put it in the mandrel. From there it was just a matter of keeping the file chalked and clean and I sat in my recliner and filed them. It took about an hour. The pictures of my tool are below. I would still like to make a tool like jay used, but even more I would like some real facts about the value of the cams in the action over the bolt lugs.

Hope this Helps Gary

Oh I do have some pictures of my action and I will try to post them later.

Gary
 

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Thanks for the pics Gary

Ive seen that tool somewhere before, probably on here no doubt, how are you controlling the helix of the cut? is it simply by hand and trial and error? do the cams come out as a true helix or as flats? Ive come up with a tool(in my head) that could cut the cams using a mill and a rotating cutter similar to Jayidaho's version, but instead of reciprecating the cutter, the cutter is spring loaded on the mandril axis and fully rotates, then cams down when needed then springs back up to clear the lug abuttment face, then cuts the opposite cam, depth of cut would be controlled using the Z on the mill, quite difficult to explain but think of a modified drill quill, hope it makes sense.

KB
 
I have posted the pictures before, but I was thinking it was on homegunsmith, anyway I just adjusted the depth by hand on mine relieving it enough so the the bolt would close doing it a little at a time on both sides. The depth could be controlled by putting a stop collar on the mandrel only allowing it to attain a certain depth.

I believe it is a helix as you are replicating a screw thread as you rotate the cutterdown into the action. I will say I recently barreled a new Savage target action and my cams by far nicer and smoother that the ones on that action.

If you can make a rotating cutter work for this I would love to see it, I have a cnc mill and I have tried numerous cutter profiles and I have not been able to make one work.

Nesika Chad posted some information saying he thought it could be done using a ridgid tapping action on a cnc mill, but my mill does not know where the spindle rotation is, just the speed.

I think it might be possible to lock the spindle and do it with a stationary cutter, but again I ended up doing simple, after all I will probably never do more than a few actions.

I have thought about possibly making some 80% actions instead of just the blanks, but I don't know if time will ever permit that or not.

Any more info on having the cams on the bolts and more ideas on how to cut them in the action would be appreciated.

Thanks Gary
 
Its just dawned on me that you are the chap advertising the edm cut action blanks! when i am finished in iraq i intend on purchasing several of them off you for myown action builds, its been about 4 years since i last came up with the cam cutting idea and had it down on paper and could'nt see any reason why it would'nt work, infact it looked like it could cut the cams and the lug abuttments at the same time, abit like taking a face cut end on of the action, with a double tipped milling cutter but cams down in the right place to make the cut of the cams............i wish i could use solid works! would be much easier to see in pictures.

KB
 
Heres a thought, just to speed things up for now, do you have access to a spark eroder(ram edm)? on your current cam cutting tool, you could spark a slot on the opposite side and use 2 file tips to shave both cams at the same time?,,:rolleyes:


KB
 
Gary, Instead of using a piece of file try a piece of toolbit 3/16th and make a guide from a piece of tubing with the angle cut then just shave a few thou at a time. Kind of hard to explain but I cut the cams for a homebuilt rimfire action that way. Jon
 
Ram EDM

KB if I had a ram EDM instead of working on the tool I would just burn the cams, I think I read that is how Jerry Stiller does it in his actions.

The file actually does plenty good for just a few actions and I really wouldn't need anything else, I really just got surprised by seeing the custom actions from earlier days with cams on the bolt and just wondered if that was just as good when it was all said and done.

It could certainly be done with a great deal of precision that way.

If you get a chance make me a sketch of your idea for a tool if you don't mind sharing. You can email it to glbreil@verizon.net if you don't want to post it. I am not quite understanding and would love to see what you are thinking.

John do you think you would have to use the tool in a press if you use a tool bit instead of the file?

Thanks Gary
 
Gary

Hopefully attached is a sketch of what I had in mind, the mandril is splined to allow it to move up and down whilst being driven by the chuck, the spring collar keeps tension on the hardened dowel as it rotates around the jig face and ramps, idealy the ramps should be made with a helical face for the dowel to follow, and there are 2 ramps and 2 cutters opposing each other, the ramp angle should be made to whatever angle you want the cams to be. You could get creative with this and put thrust bearings either end of the spring and a bronsce bushing guiding the mandril? the ramps and dowel would have to be greased up, and the whole thing run at low rpms, just clamp your action vertically to the mill table, and raise the table for depth of cut. Obviously its just a sketch and out of proportion, but you get the gist...
Ps when you start making these to sell with your 80% actions, I want royalty payments.......lol:p

KB
 

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KB that is an interesting idea it might be easier to hold the ramp set up in the mill and turn the cutters by hand.

Only two problems with the royalties, the chances are pretty slim that the 80% thing will ever come to pass and the other problem is as hard as I try I never seem to make any money.:(

Thanks for sharing and if I do ever go to the trouble of building anything to cut the cams I will share it with you.

Still wondering about the cams on the bolt, is there any real problem with it?

Thanks Gary
 
The only thing I can think of about the cams on the bolt, is obviously it reduces the bearing surface of the lug, there must be a reason for the custom action makers to go down the difficult route of putting them inside the receiver, there used to be an action, a rem clone, made by AMT I think that also put their cams on the bolt, I believe jahidaho has a couple of these..

KB
 
Gary, The setup consisted of a steel rod a slip fit in tube which is a slip fit in the action. The steel rod is crossdrilled for the cutting bit with a setscrew.
The tube is cut at a 30 degree angle or whichever angle you prefer. One end ot the tube is clamped to the rod and the other clamped to the action. The angled cuts on the tube provide the camming action. A T handle on the end of the rod to turn it while feeding inthe bit. It is just a scraping action but doesn't take long to cut the ramp. Do one side the rotate 180 and do the other. I can send you apic of what I used so maybe you can get the idea. As far as just putting the cams on the bolt it could probably be done but may cause other problems but the bolt should at least have a bevel on the corner that meets the ramp. Jon
 
Well spotted. I've had the book since the late 80s and I'd never really picked up on that.

We had a thread about cutting chambering cams in the receiver ring a little while ago over at Practical Machinist.

Some of the guys posted pictures of some simple fixtures for doing the job.

I'll see if I can find the thread and post a link to it.


the cam helix is effectively a very short section of 2 start thread, whether you

  • shave it with two cutting edges at the same time, controlled by a guide,
  • cut it as a thread on the lathe,
  • or file it by hand, checking with some sort of spotting dye, to see that both sides match

Remmington and Savage type actions seem to have ample metal in the lugs to resist both shear failure and set back with normal head diameter cartridges, so I suppose it is a preference thing, to do it the "right way" and put the cams in the receiver, even when there doesn't seem to be a problem with putting them on the bolt.
 
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