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Thoughts on replacing a BD #6 lobes with theoretical #7 lobes


Original Post
Chris Ritna · · Unknown Hometown · Joined Apr 2014 · Points: 0

I was looking at making my own #7 cam (more for a shits and giggles project than the most useful size cam). I was poking around some of the dimensions of the larger BD cams and it looks like all the cams have the same size axles (5.5mm) and same axle spacing (~36mm) so my thought was up scaling the lobe size to what a 7 would be. Lobe design set aside, what are your thoughts on cutting off the axle cap plate (plate with the stamped #6), sanding the mushroomed heads of the axles and replacing the lobes with larger ones (keeping the same spring/trigger wires). I am looking for the groups thoughts and concerns to this. 

One thought being the width bridge (spacer block which holds the axles) might be smaller than what would be designed by BD. A number 4 is ~26mm, #5 ~30mm, and the #6 is 43mm. This should only affect the stability of the cam when in a placement by increasing the MOI of the contact point of the lobes when rotated via stem movement. Increasing the bridge width would mean the need to replace the whole bridge and axle assembly (basically negating the point of lobe replacement) as there would not be enough space to fit the lobes+spacers on the same axles. This would be especially hard seeing as I would be increasing the lobe thickness from 7.5mm to 9.5mm to decrease the chances of lobe folding. I would recap the axles by tapping a small hole through the center of the axles (no more than 5mm deep) and lock tighting small screws connecting a new axle plate. 

Lobe design would basically be identical to a number 6 except the area outside of the secondary axle guide edge(?) would be scaled to fit the appropriate section of the logarithmic spiral to give a #7.

Any thoughts?

Pete Spri · · Unknown Hometown · Joined Jun 2009 · Points: 286

Can't hurt to make one and try!  If you have fun doing that stuff, go for it!  You can always buy a valley giant if you fail.


Think about making the width of the Axel a bit wider for more stability.

Tomily ma · · Unknown Hometown · Joined Jan 2011 · Points: 295

Best idea of all time!!!

Chris Ritna · · Unknown Hometown · Joined Apr 2014 · Points: 0
Pete Spri wrote:

Think about making the width of the Axel a bit wider for more stability.

Are you talking axle diameter, axle length, or axle seperation. Both diameter and seperation increases would require a new bigger bridge which would be make the use of 6 as a base more work than just starting from scratch. Increasing acle length might be possible without a total redesign but getting those axles out and more specifically new ones in without damaging the bridge would be hard. Also finding replacement axles of the right tolerances could be hard as well.

Talking on axle diameter for a minute. Theoretically, perfect loading would not lead to higher forces on the axles since load angles would all be the same and the peak and steady state forces would be the same. Placements that would rotate under loading could end up with a higher torque on the axles but that should relieve itself when the lower lobe set walks to acount for the unaligned force.

highaltitudeflatulentexpulsion · · Colorado · Joined Oct 2012 · Points: 35

It wouldn't make any sense to reuse the axle. You'd end up with an inferior axle. Grade 8 bolts and locktite. Then you've got the option of using spacers and widening the whole unit.

Chris Ritna · · Unknown Hometown · Joined Apr 2014 · Points: 0
highaltitudeflatulentexpulsion wrote:

It wouldn't make any sense to reuse the axle. You'd end up with an inferior axle. Grade 8 bolts and locktite. Then you've got the option of using spacers and widening the whole unit.

How would reusing the axles lead to inferior axles

slim · · Unknown Hometown · Joined Dec 2004 · Points: 1,107

my guess is that when you pull the trigger on the new setup, the lobes are going to hit your fingers.  that is one of the things i really dislike about the #6 WC friend - it is super annoying.

highaltitudeflatulentexpulsion · · Colorado · Joined Oct 2012 · Points: 35
Chris Ritna wrote:

How would reusing the axles lead to inferior axles

Aren't you grinding the ends off the axle to remove them? If I'm visualizing how you're going to reattach the same axles again, I think they'd be really weak in tension. 

Chris Ritna · · Unknown Hometown · Joined Apr 2014 · Points: 0
highaltitudeflatulentexpulsion wrote:

Aren't you grinding the ends off the axle to remove them? If I'm visualizing how you're going to reattach the same axles again, I think they'd be really weak in tension. 

I would be cutting the plate at the end of the axles to remove it. at this point there would still be the mushroomed heads of the axles that would stop one from removing the lobe assemblies. I would be sanding the last 5mm (+/-2mm) of the axle (the mushroomed head) down equally on all sides until it matched the diameter of the rest of the axle. The Axle would only change on the last 5mm on either side and would only loose the large diameter material. 

Chris Ritna · · Unknown Hometown · Joined Apr 2014 · Points: 0
slim wrote:

my guess is that when you pull the trigger on the new setup, the lobes are going to hit your fingers.  that is one of the things i really dislike about the #6 WC friend - it is super annoying.

Not something I thought about, will investigate (If I can without the bigger lobes) when I have a 6 infront of me


Pete Spri · · Unknown Hometown · Joined Jun 2009 · Points: 286

Length.  As cams get bigger, it is nice to have the lobes a bit farther apart to stop tipping, it helps give them some stability.  I would take the width of a #6 friend over the width of a #6 camalot any day.

caesar.salad · · earth · Joined Dec 2012 · Points: 75
Pete Spri wrote:

Length.  As cams get bigger, it is nice to have the lobes a bit farther apart to stop tipping, it helps gibe them some stability.  I would tale the width of a #6 friend over the width of a #6 camalot any day.

This

Guideline #1: Don't be a jerk.

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