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Modifying The Cams


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#1 Steve McKuhen

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Posted 11 January 2012 - 07:57 PM

Another idea to lessen the cranking pressure would be to modify the cams to shorten the amount that the bolt spring is compressed. I thought of this as I want to increase the thickness of the cocking ring to experiment with bearings on the end of the firing pin. I want to do this with out adding to the total length of the body.
I have no idea how to do this. The only thing I can think of is to eliminate one measurement in each direction as the cam is machined and see what happens.
Or just remove material from the total length of the cams but this may change the firing?
Or remove a little material from each part?

#2 Roller

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Posted 12 January 2012 - 12:25 AM

The ramp up to firing position is roughly 45 degrees which is borderline for this type of mechanism. If the ramp up could be decreased to 30 degrees it would lessen crank pressure. By virtue of the scale of our gun there isnt much room to move on this.

Frank

#3 Sparky_NY

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Posted 12 January 2012 - 11:11 AM

The ramp up to firing position is roughly 45 degrees which is borderline for this type of mechanism. If the ramp up could be decreased to 30 degrees it would lessen crank pressure. By virtue of the scale of our gun there isnt much room to move on this.

Frank



I mention that a while back in another thread but nobody seemed interested. Look at the DE and RG cam profiles and compare. The DE gun are steep fast ramps, the RG are much more shallow incline. Its any wonder the RG gun cranks easier. A side benefit would be that with a improved cam profile stiffer firing spin springs would be possible. Right now, stiffer springs make it too hard to crank. Its not a radical mod to make a "improved" set of cams. (especially if you have cnc to cut them!) I already had this planned to do.

#4 Steve McKuhen

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Posted 14 January 2012 - 05:51 AM

Sparky,
My interest in the cams goes back to the beginning of my firing problems. Mr. Schneider says that if the cams are not made following his instructions there will be serious binding. They were the first thing I checked. I even talked to Mr. Schneider about them. The conclusion was as Roller says that there is not enough room.
In order to try a bearing idea I need to gain some room in the cocking ring. I thought some of this space could be gained by shortening the overall cam length. This could be done by cutting off the two ends or maybe changing the angle. Then I went back to the discussion I had with Mr. Schneider and thought that an advantage to changing the angle could be a little gain in cranking.
Since you had already planned on doing this using your cnc machine LOL please show us the successful results.

#5 Sparky_NY

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Posted 14 January 2012 - 12:49 PM

My gun is about 85% complete, the cams (standard D&E) design are complete and installed. About all that is left is the bolts and cocking ring, and a few cosmetic trimmings. All the bolt internals are made as are the bolt blanks. I made one bolt completely for test purposes. The problems with the extractor design were obvious. I have known of the issues with the D&E design since I started. I too talked with Doug on a few occasions but it quickly became obvious that no solutions to the well known problems were going to come from him. Doug, who I really liked, strongly stood by his designs even though there has never been a firing gun made from them.

I was not about to reinvent the wheel. Manually operated firearm design has not really seen any changes in the last 100 years. Things such as solid designs for firing pins and extractors are history. Only recently I had the opportunity to closely look over a RG gun which does not share the design flaws of the DE gun. I was amazed how easy the gun cranked and smoothly. Of course I noticed the conventional extraction methods as well. A quick look at the RG guns cam profiles and it became obvious why the gun cranks so nicely.

There are excellent pictures here on the forum of both the RG and DE cams. Pretty obvious why the RG gun cranks so nicely. Because of the less radical slope on the cams, the RG design might allow stiffer firing pins springs to be used also.

Yes, I have a cnc mill that I retrofitted completely so remaking the cams is a fairly easy task for me. I would be far less willing to remake the cams if I had to do it manually, its a lot of work. The gun is a winter project for me. As soon as I finish up a cnc lathe retrofit, its back to completing and firing the gun. I hope start again in the next couple of weeks. The plan of attack is pretty clear.

How far along is your gun?

#6 Steve McKuhen

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Posted 29 January 2012 - 04:15 AM

This is the first attempt to modify the cam angle. Only the first side of the rear cam was changed. This is the side that cocks the firing pin. It is an improvement. I do not have a torque wrench yet to take measurements.
Roller, does your gun fire at the 6 o'clock position? My fires at about 5:30. If I cam move it to 6 I can add a little more length to the cam. I am also going to make the transition point more gradual instead of a sharp corner. I have some more ideas to lessen the cranking pressure but one thing at a time.

Original cam with four bolts, the lugs are blued
Attached File  DSC00093-id=727.JPG   28.9KB   0 downloads

X-1 cam with four bolts, easier to crank
Attached File  DSC00094-id=728.JPG   32.01KB   0 downloads

Original cam on the left, I blued the modified surface
Attached File  DSC00097-id=729.JPG   19.01KB   0 downloads

X-1 cam on the right, angle is less steep, longer
Attached File  DSC00098-id=730.JPG   21.47KB   0 downloads



#7 Roller

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Posted 29 January 2012 - 03:11 PM

Steve,

That's exactly what I was thinking for reducing the cam angle. When you get your wrench it will interesting to see the numbers for cranking force. I am not sure at what position my gun fires, as I have been behind it and shooting 8' away. When I get it back together I will take a look. If I had to guess I would say it fires between 4 and 5 depending how fast the cranking speed is.

Frank

#8 Steve McKuhen

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Posted 29 January 2012 - 07:20 PM

I was able to make the second cam transition much better and a little longer. Changing the position of the gap changes the position of the firing. I think I only need one more cam to have the best solution.

Cam X2 is on the left. The blue marked area shows the longer length and the more smooth transition. X1 is on the right.
Attached File  DSC00100-id=731.JPG   21.76KB   0 downloads



#9 Steve McKuhen

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Posted 30 January 2012 - 05:57 AM

Changing the position of the gap changes the position of the firing.

This is not correct. The firing position is controlled by the cocking ring. I am using an old ring that still has threads on it. It had slipped in the stand and I did not notice it. I am using this ring because it allows me to test different size firing pins.

#10 Steve McKuhen

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Posted 27 July 2013 - 05:16 PM

To answer Steelcrafter's questions about the cams
I decided to make several more as I have not been
able to find my notes.

When I made my first cam I was filled with anxiety because
the instructions said that they must be made following the
instructions or serious binding would occur. I have since found
that not to be the case. I did not like the mandrel method so I
just put the blank in the chuck. The dividing head does not
need to be indicated perfectly. As you proceed to plunge it is not
necessary to be 100% accurate in your count of holes and
moving the table. For instance, if you want to move the table 0.001
and move it 0.002 instead, do not go back. Just plunge the hole
and advance the next hole on the dividing head and plunge again.
Advance the head to the next hole then advance the table to the
next increment, which would be 0.003 in this example.
I have scribed lines on the cam and used 30 deg
divisions so it is not necessary to keep count of the number of
holes on the dividing head. In my first attempt I used dails to
keep track of the table movement. I have since added Igaging DROs
to my mill. Cutting the cams this time was much easier.
It took me 20 minutes to plunge through one 30 deg section. I did not
keep track of the entire process.

Blank mounted in the dividing head.
Attached File  DSC00272-id=1367.JPG   28.68KB   0 downloads

I scribed lines every 30 deg from 0 to 180. Also
at 155 deg and 205 deg. The lines are difficult to see
but are marked with a black number. These lines were
so I could visually check my calculations. They are not
necessary to cut the cam. I took more pictures
but they were not clear.
Attached File  DSC00273-id=1373.JPG   29.5KB   0 downloads

I drilled an entry hole at 0 deg, 0.348 from the edge.
Then drilled at 180 deg, and 25 deg on each side of 180 deg.
These holes are 1.263 from the edge.
Attached File  DSC00282-id=1369.JPG   28.45KB   0 downloads

I set the dividing head at the 25 deg hole on the left side of the blank, 155 deg,
and began plunging 0.003 per hole until I reached the 30 deg line at 150 deg.
This is easy to locate as the head has locating holes every 30 deg.

I then plunged on at 0.002 every hole until I reached 120 deg.

Then plunged 0.001 per hole until 90 deg.

Then 0.001 per hole until 60 deg.

0.001 per hole until 30 deg was reached.

And finally 0.001 per hole until reaching the entry hole at 0 deg.
I then turned the dividing head handle to cut around the blank at 0.348
leaving enough material to finish from the other direction after
the opposite side of the cam was cut.

Then I set the dividing head at 25 deg after 180 deg ,205 deg, and plunged
at the recommended 0.005 per hole. I did not keep track of the
number of holes as I could watch the DRO until I came to 0.0348.
Rotating the dividing head completed the 0.348 cut.
Attached File  DSC00283-id=1372.JPG   28.52KB   0 downloads

I moved back to the entry hole at 205 deg and rotated the
dividing head until the cam was cut off.
Attached File  DSC00284-id=1371.JPG   27.54KB   0 downloads



#11 Steve McKuhen

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Posted 27 July 2013 - 05:36 PM

I cut out the 0.520 entry groove.
I refined the edges of the cam with varies
files to eliminate any rough spots. Round over
the top, sharp edges of the cam. Relieve
the edges.

The space to the right of the entry groove will
not measure 0.348, it will be a larger dimension
depending how accurate the plunges are made.
Remove the excess material up to the first 30 deg mark.
Then blend in so there is no abrupt change.

I do not know the steel quality of my blank. It came from
an hydraulic cylinder casing. I heat treated it to harden
the edge of the cam that was modified to lessen the
friction from the lug.

The bolt lug will also be hardened.

The finished cam.
Attached File  DSC00285-id=1374.JPG   16.48KB   0 downloads



#12 Steelcrafter

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Posted 27 July 2013 - 09:58 PM

Hey Steve,
Thanks for the detailed step by step instructions of your cam mod! You can definitely tell the difference between your cam and the original. By varying the amount of table movement through the angle, you're creating a slight concave profile to the cam. Awesome! How much improvement did you see with this cam mod?

I had another thought on improving the friction generated between the bolt lug and cam angle. A small say, 1/8 diameter roller could be installed in the corner of the lug that tracks along the cocking angle. This would be akin to roller cams in performance engines. Of course it would greatly increase the complexity of the bolt build.

Dan

#13 Steve McKuhen

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Posted 27 July 2013 - 11:56 PM

You seem to be a step ahead of me.
When I get to the point of completing the new
bolts I intend to give instructions and pictures
of just such a modification. As a roller I used
miniature ball bearings mounted on a stud
cut with a trepanning tool.
The bearing needs to be located so it does not
extend pass the edge of the lug. The lug must absorb
the shock of the firing. Have not finished testing this.
Am concerned about removing too much of the lug.
I am describing just the cam so it may be used with the
recommended bolt lugs. I am also suggesting that the
lugs and the cam be hardened.
I also tried to replace the lug with a larger bearing.
It worked great for three rounds and then the mounting
stud would break as there is just not enough material left
to absorb the shock.
I have experimented with other modifications that I will
mention as I continue my post of the re-build.
Slow progress.

#14 Steve McKuhen

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Posted 28 July 2013 - 10:25 PM

The remainder of the blank makes the front cam.
It saves some time as one side of the cam is
already cut.
Attached File  DSC00286-id=1375.JPG   30.62KB   0 downloads

I set the dividing head to 0 and rotated the blank
so that the apex of the angle was below center.
I scribed lines at 0 deg, 48 deg, and 96 deg.
The 48 deg mark becomes the 0 or center line.
Attached File  DSC00287-id=1376.JPG   30.07KB   0 downloads

I reset the DRO to the edge and began cutting
at the 96 deg mark.

Attached File  DSC00288-id=1378.JPG   30.43KB   0 downloads

I plunged away at a leasurly pace of 0.005 per
dividing head hole until I reached 0.915. Again
this took about 20 minutes to cut the angle.
Had a few sips of a Diet Coke along the way.

Attached File  DSC00289-id=1377.JPG   30.64KB   0 downloads

Then continued the cut with the dividing head handle
until I reached the other side.
Attached File  DSC00290-id=1379.JPG   32.12KB   0 downloads



 



#15 Steve McKuhen

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Posted 28 July 2013 - 10:39 PM


Parting off on the lathe.

Attached File  DSC00291-id=1380.JPG   39.57KB   0 downloads

After parting I again checked my measurements,
refined the edges and removed the burrs. Rounded
over the top sharp corners. The only modification to
this cam is to remove a little material opposite the rear
cam at the entry groove where the new angle starts.
I hardened the edge that the lugs rides against
as it returns. This would be the left side? I cleaned
it up and blackened it.

The finished cam.

Attached File  DSC00292-id=1381.JPG   18.97KB   0 downloads



#16 Steve McKuhen

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Posted 29 July 2013 - 10:50 AM

Improvement to the rear cam.

I have since thought that by extending the 0.002 cut past the 30 degree mark for another 15 degrees would provide the flat spot to the right of the entry slot and make filing and refining easier.

The first increment of the 0.001 cut would be shortened by 15 degrees and the last 0.001 cut would again stop when 0.348 was reached.




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