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Hardening ball on end of fine threaded stud

jim rozen

Diamond
Joined
Feb 26, 2004
Location
peekskill, NY
Why not just buy the steel ball in the correct hard state? I suspect he does not want the 'shade tree mechanic' version of heat-treat.
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
Thx all for the suggestions. I think I’ll try W1 starting with 3/8” rod, turning the ball end then turning the rod to the 5mm OD for the 0.5 threads and then hardening the ball end as many suggest.

As for the application, this screw & ball will be an adjusting screw pushing against a valve lash cap in a 210cc 4-stroke motor that is turning over 8000 rpm. The existing adjusting screw is not surviving.
 

MrWhoopee

Hot Rolled
Joined
Nov 8, 2017
I don't want to discourage you, but in this application if the original is not up to the job you may be hard pressed to improve on it. How is the original part "not surviving" and how long has it been in service?
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
The original adjustment screw was designed to run at 7 hp and 2700 rpm. Now that it is been modified to produce over 20hp and 8400 rpm it is far beyond its original design requirements. The contact surface is 5mm and was meant to “rub” while pushing a valve stem through a very small arc. The greatly increased valve lift also greatly increases the rub “length” wearing out the tip of the screw. The arc is now high enough that the screw tip is almost to the edge of the valve tip and the flat tip of the screw is at an angle so the contact surface is very small. Large force on a small surface…you get the idea! The ball end with twice the diameter of the screw is an attempt to reduce wear by increasing surface area throughout motion and keep the pushing force in a desired down direction
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
Just wanted to make sure you motor-heads out there weren’t wondering why we don’t develop a roller rocker valve system…there just isn’t enough real estate to do that and designing and casting or machining a custom head is just not financially viable!!!
 

dgfoster

Diamond
Joined
Jun 14, 2008
Location
Bellingham, WA
Dan,

This application involves pretty intense shock (4000 times a minute---half the crank RPM) and wear. So, the ideal tool steel may not be O-1. I do not have enough tool steel knowledge to state what woud be the ideal choice. But I do know S7 has excellent shock strength. It sounds like fracture failure would be a very undesireable outcome for the part you are making. Hopefully someone here will know what the best alloy choice might be.

"It features excellent impact and shock resistance and decent resistance to softening at high temperatures. S7 is comparatively less resistant to wear but is very tough. It resists distortion during heat treatment well."

Pics of the worn part?

Denis
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
Dan,

This application involves pretty intense shock (4000 times a minute---half the crank RPM) and wear. So, the ideal tool steel may not be O-1. I do not have enough tool steel knowledge to state what woud be the ideal choice. But I do know S7 has excellent shock strength. It sounds like fracture failure would be a very undesireable outcome for the part you are making. Hopefully someone here will know what the best alloy choice might be.

"It features excellent impact and shock resistance and decent resistance to softening at high temperatures. S7 is comparatively less resistant to wear but is very tough. It resists distortion during heat treatment well."

Pics of the worn part?

Denis
Thx Denis,

As long as a fractured part doesn’t wind up where it will cause damage it would probably result only in no valve lift! But we know Murphy’s law is called a “law” for good reason and the fractured part would then land where it would cause maximum damage!!! I’ll look into S7 as I have not worked with it. With the larger surface area of the ball end compared to stock I’m hoping wear will be reduced so toughness against fracture is desired. The cost to fab these is minimal so even if wear was significant they can be replaced often.
 

atex57

Hot Rolled
Joined
Sep 6, 2006
Location
SW Wisconsin
As others above suggest, tell us all the details.

Can you put a different radius on the contact area? A mushroom head may give better contact area and less PSI.

Seems in this case the easiest would be to make the threaded end, then clamp on that, then turn the contact end.

Ed.
 

Pattnmaker

Stainless
Joined
Nov 2, 2007
Location
Hamilton, Ontario
Only suggestion I would have is if you are going to use W1. I would harden it in oil. That small a part will harden properly in oil and is far less likely to crack in oil.

I used to make an industrial chisel/scraper out of W1 they tapered from 1/2" to 3/8. I would have a couple out of 50 crack in ht. So I sent a batch out to a ht shop as I knew their temperature control was better than mine. About 10 came back cracked. An experienced friend suggested an oil quench. After hardening and tempering I took one and using carbide machined to the center of the chisel to ensure through hardening. It was just as hard in the centre in the high 50s rc.
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
Is it better if the ball wears or make it harder the the part it rubs wears instead. Which is easier to replace when worn?
Bill D
Replacing the ball/stud is a 5 min job so super easy. The lash cap that the ball rides on is easy too but more costly to produce
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
As others above suggest, tell us all the details.

Can you put a different radius on the contact area? A mushroom head may give better contact area and less PSI.

Seems in this case the easiest would be to make the threaded end, then clamp on that, then turn the contact end.

Ed.
You are correct in that a full ball is not actually required since the contact arc is way less than a sphere. I would probably grind a tool to just do a 5 mm radius hemisphere on the end and then use a tool on the back side of the hemi to gently blend to the 5mm threaded section
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
Only suggestion I would have is if you are going to use W1. I would harden it in oil. That small a part will harden properly in oil and is far less likely to crack in oil.

I used to make an industrial chisel/scraper out of W1 they tapered from 1/2" to 3/8. I would have a couple out of 50 crack in ht. So I sent a batch out to a ht shop as I knew their temperature control was better than mine. About 10 came back cracked. An experienced friend suggested an oil quench. After hardening and tempering I took one and using carbide machined to the center of the chisel to ensure through hardening. It was just as hard in the centre in the high 50s rc.
That’s great info…thx
 

DanBrub

Aluminum
Joined
Feb 14, 2019
Location
Tennessee
Wanted to end this thread showing the results of the attempt to follow a number of excellent recommendations. I used a 3/8 dia W1 annealed rod and turned the threaded portion to size leaving a 1/16” radius where the ball end started and ran the M5x.5 die to cut the thread. Cut the rod leaving enough material to form a 3/16” radius hemisphere on the ball end and turned that with a radius tool while holding the threaded length in collet. Next I drilled a 5mm hole in a 3/4” dia piece of 1018 steel deep enough so that just the ball end plus around 1/8” of the threaded portion protruded. I hoped that as I heated the ball end the threads that were in the hole would be protected. Heated the hemisphere fairly quickly to minimize heat to the threaded length and then quenched in oil. Don’t have hardness testing equip but file wouldn’t touch it. Polished the hemisphere and reheated slowly till straw color to temper.
 

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