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Clutch Fork

RobinHood

Active Member
Premium Member
#1
This is out of my new (new to me) lathe project. I has a worn clutch fork made from cast, then machined bronze.

1st pic is the basic set-up of the fork and the hardened shift sleeve. Both fwd and rev clutches are visible.
IMG_0189.JPG IMG_0193.JPG IMG_0194.JPG IMG_0195.JPG IMG_0196.JPG

I was just going to make a new fork, but when i started looking into the price of bearing bronze, that thought quickly vanished and i am now contemplating a) repair or b) make new from steel and use small bronze pads as wear contact surfaces.

a) For the repair, i was thinking Al/Si bronze braze or TIG build-up the old fork and then re-machine. It does not fix the poor fit (see 2nd pic from left) which probably caused the uneven wear in the first place.

b) Making a whole new fork from steel with better fit would solve the uneven wear issue (i think). I would braze or TIG the Al/Si bronze wear pads onto the steel fork. You can see the contact wear pads at the end of the fork in the 4th pic from the left. The 5th pic has the worn out pad clearly visible.

My main concern in either case is the heat input which could cause distortion and wreck the part.

Another option might be to use bronze welding wire as "rivets" evenly spaced around the fork as wear points.

What are your thoughts?
 

Bofobo

Well-Known Member
Premium Member
#2
Get some sacrificial scrap bronze and using the part as a guide make a pattern, then cast the old part into the new one. If you mess it up in machining, cast another one.
Thats my thought on it anyway. Looking forward to other input
 

RobinHood

Active Member
Premium Member
#3
I like your idea Bofobo. The thought has crossed my mind. I am just not set up for casting anything at the moment. It would be fun to do for sure.... Too many other things on the plate right now.
 

Dabbler

Well-Known Member
#5
I like your steel idea with bronze 'shoes'. How about getting some bronze plate, making semicircles, and then attach via TIG brazing through holes in the semicircles? are these yokes easily removable for maintenance, or dies it need an act of parliament to get to them?
 

RobinHood

Active Member
Premium Member
#6
OD including the pin is ~ 4”. The fork is just over 1/2” thick.

9C2BA7C1-4604-4F35-AC77-74F1C018A29A.jpeg

I plan on adding the second half for extra stability and aligmnent of the fork in the shift sleeve. There is lots of room in the head stock for it. Kind of like a connecting rod attaches to a crank journal, but with more clearance.
 

PeterT

Ultra Member
Premium Member
#7
I know from personal experience bearing bronze can be spendy depending on the flavor & size. It can be purchased in plate form in smaller chunks which might suit your needs. With some bandsaw work you could pre-cut the extremities & some of the ID to harvest some usable chunks for another project.
https://www.onlinemetals.com/merchant.cfm?pid=15928&step=4&showunits=inches&id=1165&top_cat=850

in rod form it kind of max's out at 2.5" again depending on supplier & alloy flavor
https://www.onlinemetals.com/merchant.cfm?id=1060&step=2&top_cat=850
 

Johnwa

Active Member
#8
I’ve got a piece that I assumed was bronze but it’s a lot yellower so is likely brass.




Sent from my iPad using Tapatalk
 

RobinHood

Active Member
Premium Member
#10
I know from personal experience bearing bronze can be spendy depending on the flavor & size. It can be purchased in plate form in smaller chunks which might suit your needs. With some bandsaw work you could pre-cut the extremities & some of the ID to harvest some usable chunks for another project.
https://www.onlinemetals.com/merchant.cfm?pid=15928&step=4&showunits=inches&id=1165&top_cat=850

in rod form it kind of max's out at 2.5" again depending on supplier & alloy flavor
https://www.onlinemetals.com/merchant.cfm?id=1060&step=2&top_cat=850
Thanks for the links. Do you have any experience ordering from them and shipping to Canada?

I have acess to an account with McMaster Carr, but i never had them ship to Canada either as i heard that can be costly. Any experience?

Good point using flat bar....
 

PeterT

Ultra Member
Premium Member
#11
Yes I have used OLM on several occasions. They discount the UPS shipping to Canada (unless something changed in the past 4-6 months) compared to other USA metal vendors like say Speedy Metals. I'm not sure what the savings amounts to but might be 20%. You can see shipping cost at check-out. Now with all the tariff BS, could be things are a bit different but that would apply universally from anything USA. OLM is good for small sticks of more specialized alloys which is kind of my issue in a nutshell.

If you have an active McMaster account & they will ship to you, that is like gold. They stopped shipping international to common mortals maybe 10 years ago citing too much NAFTA paperwork. No way around it, they even detected our CDN credit cards even if we specified USA ship destinations (like a buddy). However I am aware they still ship to company type accounts, educational facilities etc. I cant comment on shipping modes but guessing they prefer the couriers. But they are such awesome 1-stop shopping, even if you had it shipped via UPS drop that would be well worth your while. I recommend DYK shipping for that unless you have border connections. Basically DYK provides you a 1-time Sweetgrass MT address (not a PO box). Vendor ships there at typically lower rate because its all inside USA. DYK trucks daily from MT location to Calgary, you get a call for pick up & they charge a fee of course but its reasonable.
 
#13
Car guy talking...keep that in mind. I think your current fork did exactly what it was designed to = sacrificial. I think you can fix what you have. Shift fork currently looks like what automotive standard light duty/car tranys use. I have just freshened up a trany rated for 600ftlbs/tk. It uses similar looking cast steel shift forks, but with clip on pads originaly plastic. I have upgraded to brass. The pads are about .750" in length and inside channel likely .250" to .312". These pads are intended to be sacrificial, but do sustain substantial load, I have yet to have one fall off, if that is a concern.
Google a Munci M21 shift fork for a look. Furthermore a Tremec TKO 600 shift fork brass pad. The TKO is the one I have just completed, and I have a new unused pad I could bring on Saturday to Modern if you want a look. These brase/bronze pads are an aftermarket machined piece, you can make them any size to repair your current fork. I might have some material...Free. Working nights so my response will might be slow!
Thanks, Todd T.
 

John Conroy

Well-Known Member
Premium Member
#14
If you want to make a new steel part I have some 4 inch 4140 tool steel round bar stock. I could bring a slice of it on Saturday if you want.
 

PeterT

Ultra Member
Premium Member
#15
I'm not exactly sure which are the worn surfaces, but any chance of silver soldering bronze sheet to them slightly over thickness & then re-machining true? If it were on one of the main faces you might have a fighting chance, but if its in & around the step, probably not feasible. I have seen this 'skinning' method with copper over steel laps which would probably be a tougher environment from a shearing standpoint, but admittedly I'm on uncharted waters.
 

Attachments

RobinHood

Active Member
Premium Member
#16
@PeterT : thanks for all your info regarding OLM - they will be my second choice if McMaster does not work out. I have to be nice to our S&R guy and hopefully i can put the order in through the company account. I do have a personal account, but as stated, have not shipped anything to Canada for fear of losing it.... i usually ship to a place in CA and pick it up personally while on the road for work. No trips to CA in the near future, unfortunately.

@turner : thanks for your valuable input as well. Yes, the fork did do its job and sacrificed itself. It is a poor fit at best from new and wore out way too fast. The wear pads are just making contact with the rim of the shift sleeve because the inside radius of the shift fork is too large and does not engage well in the groove.
I would appreciate a look at the Tremec fork pad.

@John Conroy : thanks for your offer as well. I do have 4” 4140 myself, so i am covered in that department.

I am going to bring in the parts to Modern Tool on Saturday for your examination. Sometimes the pics don’t show all the details even though i tried to take them so they would....
 

RobinHood

Active Member
Premium Member
#17
I'm not exactly sure which are the worn surfaces, but any chance of silver soldering bronze sheet to them slightly over thickness & then re-machining true? If it were on one of the main faces you might have a fighting chance, but if its in & around the step, probably not feasible. I have seen this 'skinning' method with copper over steel laps which would probably be a tougher environment from a shearing standpoint, but admittedly I'm on uncharted waters.
We’ll call this the good side. Notice how the wear pads at the end of the fork are even in shape and colour.
1547086283037.jpg

Now for the bad side. The top pad is completely gone as far as its depth goes and the wear is even into the fork body itself. The shiny narrow sliver on the top tine is what’s left of the pad. You can also see the radius of the shift sleeve as it compares to the radius of the fork. They just don’t match.
1547086595168.jpg

Here is the end view
1547086916909.jpg
The bottom tine is about normal in width for its age (30 years) with still plenty of wear pad material remaining on either side. On the top, the left side is much like its brother on the bottom left: in good shape. The right side top is the problem because the pad material is all but gone where the fork rode up and partially out of the groove and only contacted the shift sleeve on only about half its area. You can see how the shift sleeve ate part of the fork as well. See the slanted line from bottom right to top. The step in the top right pad is all the material that is missing.

Hope this explains it a bit better.

So repairing the faulty design is not going to fix the problem long term: it will wear exactly the same way again. Redesigning the fork to properly match the groove will make it last.

Why is this such an important part? The fork needs to engage the FWD and REV clutches properly so that they don’t overheat and burn out. The manual specifically warns about over-adjusting the clutches (that’s what folks seem to do to compensate for bad spindle speed pick-up). No amount of clutch lever adjusment is going to fix a bad fork.
 

PeterT

Ultra Member
Premium Member
#19
Just catching up on my Youtube channels. Interesting one by Tom Lipton venture into 3DP metal. Happens to be a different alloy for his purpose but got me thinking about your clutch fork. I have zero experience with Shapeways bronze in terms of suitability to this application. But company wise, my one & only plastic part order came through reasonably priced with no drama. I wonder if it was printed slightly oversize to compensate for any 3dp striations & allow final machining dressing allowance might be competitive option to a chunk of bronze stock from scratch since the overall volume isn't too great. I don't have a good feel if the sintered material would be as good as stock alloy in this maybe kind of heavy application. Some have mentioned 3DP metal has micro porosity. I will do the CAD file to obtain price estimate if you are game.

material
https://www.shapeways.com/materials/bronze

video
 

RobinHood

Active Member
Premium Member
#20
@PeterT : what a great offer doing the CAD file. I think i am going to take you up on that, just to see how much it would be. Once i have the new fork made, we can see what you would need in order to design the part.

As far as the fork itself: i decided to make it out of steel with bronze wear pads. The pads will be silver soldered on. This allows me to use bronze that i have on hand. The steel will give me high strength. If,at some time in the future, i have casting capabilities, i will consider using this new fork as a mold and remake it out of bronze.

I decided against a repair because the fork is just such a poor fit. Also, reading on various welding forums, heating up bronze for brazing can be problematic since the alloying elements melt at different temperatures and quite often one ends up with a structurally weak spot. Silver soldering foregoes that problem for the most part. So if i’m going to silver solder, i may as well solder bronze onto a well fitting fork made from steel...

More on my progress soon...