Gatlinggunforum
General Category => General RGG Guns/ Homebrew gats => Topic started by: barrelguy on November 24, 2020, 09:34:05 AM
-
I finished up a couple of guns a year ago but was not really happy with the force required to cock the bolts. It took 5 to 7 lbs of force at the end of the
handle to cock and fire. After thinking about it for a year I decided to try and fix the problem and the logical solution was to replace the .188 brass cam follower
pin with a 3/8 dia. cam follower bearing. I made two new barrel cams with a .387 cam track and installed 3/16 x 3/8 x 1/8 radial cam follower bearings
on a couple of bolts and tried it out. The cocking force dropped from 7 lbs. to 2 lbs. Now I think the guns may be fun to shoot.
-
The more I play with it the easier it cranks. The force is down to 1.5 lb. which figures out to 6.75 in. lbs of torque.
-
Do you have a part number for what cam followers you used?
-
I could not find factory cam follower bearings with a shank I could use so I made them. I used a 3/16x3/8x1/8 metal shielded bearing R166-zz.
The ID is 3/16 +.0000/-.0002. The shaft is made from a 3/16 +.0002/-.0000 18-8 SS dowel pin which is machinable. Pins are available from
McMaster-Carr. That gave me a nominal .0002 press fit bearing to shaft. The pin figures out to be .250 long with .090 of 10-32 thread.
I got the bearings from Fast Eddy Bearings in CA for $0.99 USD ea. Sometimes it pays to shop around! I also cut a .045 wide x .045 deep
scewdriver slot on the top end of the pin for installation.
-
WOW, down to 1.5 pounds of torque. That is well worth the modifications needed to upgrade the followers. Did you have to actually make new box cams, or could the gap just be widened a little each way I wonder? If so, using cutters one piece bolts having the follower pins machined into them already a bearing could be pressed onto that pin. You might be onto something here barrelguy. Thanks for trying something new and sharing it with us here.
bruski
-
You could widen out the cam track in the existing box cam but I decided to save that cam if this idea didn't work out. The cheap chinese bearings didn't
work. The outer race broke on 2 bearings so I am looking for a stronger bearing. I am dealing with several bearing houses on the problem.
-
I wonder if your cam followers are taking up some of the recoil beatings. Is your cocking ramp rubbing the bolt backside on bottom dead center? If it is not touching the rear end of the bolt at BDC when the hammer is released then that might be a problem.
bruski
-
I forgot to mention that a quick fix for that would be to re-leave the cam slot a little bit on BDC as the recoil plate will hold the bolt forward on BDC.
bruski
-
Hi Bruski, I just splattered the gun again this morning to get ALL the broken bearing parts out of the mechanisim and there seems to be adequate clearance
around the bearing in the cam track while the bolt is resting on the cocking ring but thanks for bringing that up. It has been my experiance that some
Chinese manufacturers have metalurgy problems which could be why these bearings broke.
Thanks again,
Elmer
-
That is right, there quality control is not so good on some products. Let us know when you get some USA bearings or equivalent.
bruski
-
The latest chapter in the continuing saga of the hard cranking gun.
I got new domestic made bearings from Impact Bearing in CA No more bearing breaking problems. The new bearing number is SR166zz, $4.55 ea.
The cranking force leveled out at 2 lb. of force at the end of the handle or 9 in. lbs of torque at the shaft. That gave me an honest 60% reduction
in cranking force. My goal was 50%.
I would like to address an earlier question about doing this to Cutter's one piece bolts. To get a proper press fit on a bearing, in my opinion, the pin
dia. should be .1876 +/- .0001. Can that be done on these pins?
-
I would like to address an earlier question about doing this to Cutter's one piece bolts. To get a proper press fit on a bearing, in my opinion, the pin
dia. should be .1876 +/- .0001. Can that be done?
While it won
-
Hey oxford, try replying again, it did not come thru.
-
I only measured one of them at .188 so maybe with a little polishing they would work.
bruski
-
First gun functions fine, shoots fine, now working on the second gun. It has come to mind that I am going to end up with a couple of box cams
with a .200 wide cam track that are excess to my needs. Does anyone out there have any idea what the going rate on one is? All turning, milling,
and drilling and tapping done.
-
While it won
-
My eng. change order using radial bearings just crashed and burned. Broke another bearing. So, on to rev. D which would be replacing the radial bearings
with a 660 oilite bronze bushing floating on that 3/16 dia pin. Maybe???
-
Maybe some sort of a needle bearing.
bruski
-
I agree, it should be a needle bearing but I looked and looked and could not find one that was thin enough. Cam followers on the marketplace are all
needle bearings.
Here is where I am at. With radial bearings, force is 2 lb. With a bronze bushing, force is 2.5 lbs. With heavy firing pin springs, force is 3 lbs. (had
ignition problems). Still show about a 50% gain. Better than it was.
Note: installing a bushing makes it easy on Cutter's bolts.
-
For what it’s worth
One common reason for hard rotation in the cocked position is
the cam path was not cut to the center line. If it is off .005/.010
the hammer shaft, spring, and shear will all create friction plus, putting
more pressure between follower and cam
-
Cutter, all comments are worth considering. If the .925 dim. to centerline of the cam path is correct I should be ok. I cut the path on a Sip Jigbore
with .00005 resolution.
-
Sorry
I should have stated radial tolerance , not linear.
-
Further testing proved me to be wrong. Once the ball bearings failed and I used the bronze rollers I am about back to where I started from.
Rev. E is increase the crank handle length from 4.625 to 8.000. Oh, well, I tried. It sure seemed to be a good idea at the time.