Brass Questions...

joezmam367

joezmam367

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good morning all,

I'm currently working on an old motorcycle im restoring and have yet to come across an actual answer to any of my questions regarding brass so i thought this would be a good place to go.

1- is there a general rule of thumb on using home made brass nuts on brass rod? This would be for shifter and brake linkage paired with 2 RH M8 hiem joints, the only reason being that a LH die is crazy expensive.

I'm mostly concerned with safety on this one, i can reuse the OG parts, but brass looks so nice with black and polished aluminum.

2- tapping & thread cutting with a die.. the lathe i have access to is older than dirt, and very poorly maintained as it has little use in our shop (I have been given approval by my plant manager for government work as long as im off the clock) that being said, i'm having a terrible time with this. I've always been told stock size should be what ever thread size your shooting for before cutting (M8=.3145 stock and so on) but i found that cutting about .015 off of it prior to a die makes it much easier as im doing this by hand, thoughts on safety of this?

for anyone asking, im using 360 half hard brass

thanks in advance for any clarification on these questions
 
I don't know exactly what you are replacing with the brass, but it is not as strong as steel. I don't know if I would use it for brake linkage or shifter linkage. I would be concerned with bending or breaking . It will certainly break easier. But, to answer your other question, the rule of thumb , I believe, is if you are single pointing threads, you start with the full diameter. If using a die, you should be a few thousandths smaller in the thread area. .015 sounds like a bit too much though. There are formulas and different discussions on this on the web and you can find many different answers. I usually turn the thread area down between 5 and 10 thousandths ( I start with 5). Using a die on full diameter can result in torn threads and unusable part.
 
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From checking many bolts through the years, most threads seem to be .003 - .005 under. When strength of thread is needed I usually do not go under by more then .005. Even when using a die.
As far as brass I would not use it where any strength or possible constant adjustment is needed.
 
to give a little more info, both linkages are straight shots, no bends or kinks at all
I'll give it a go at .005 under size and go from there, hopefully the threads come out nice and stout

u/rgray why do you say yes to shifter but no to break? The brake linkage is a bit smaller, still going to go with M6, which is bigger than it is now, currently it sits at 3/16 stock.
my thought was beefing it up would prevent any issues down the line.

as a side note u/billh50 I'm planning on using lock nuts with these and should not have to be adjusted more that a fine tune now and then. as far as strength goes, becasue these are straight shots, i don't think with the pivot points it should be under much stress

here's a pic i pulled up on google to show what I'm working on. the hiem joints and original arms will be reused

ex linkage.jpg
 
joezmam367 said:
u/rgray why do you say yes to shifter but no to break?
Click to expand...

I'm thinking in a panic braking issue it would be horrible if the linkage pulled apart. If you failed the link on the shifter it would not be so bad as you could manually put it n 2nd or 3rd and limp home.
Also thinking the shifter would never have a time it would be used as forcefully as a brake. Stainless rod might be a better choice for the brake rod.
 
If the brake rod is being pushed rather than being pulled it may work. If it is being pulled then there is the chance that the threads may not be strong enough with brass and they can just strip. Especially in any kind of a hard stop such as a panic stop.
 
that has been my main consideration as well. I have seen some brass linkage kits sold online for a pretty penny, but they don't list what the actual material is either.

The brake linkage is a push style, but before putting it on, I plan on making a test rod, basically a first run complete part and ill put it in a small press, I'm not sure what the full pressure would be in riding conditions under and emergency situation, but if it can handle a half ton i think i'll be ok.
 
It's a leaver. Measure from the pivot to each working end. If long end is 6" and short is 1" then 6/1 leaver so a 200 lb push gives 1200 lb.
Not sure what and emergency panic stop would amount to lbs wise. but I would think less than 50 lbs would lock the rear tire.
I'm assuming mechanical brake if it's hyd then figures might be different.
 
It is indeed a lever brake. just springs and pads inside the hub.
the longest end is at the hub pivot, which is roughly 5 inches, short is roughly 2.5 so to be safe ill use 75lbs as a "lock up the rear tire" figure
so 5/2.5=2
2x75=150lb correct?

never thought about it this way, but defiantly an useful formula there!
 
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