Deckel FP3 L : Input Shaft & Pulley Repair

[RobinHood]

That would work - there is plenty of room behind the OE pulley for something like that. Also, there is a lot of meat on the pulley/hub to get creative. A counterbored pulley on the inboard side would also shorten the length of its keyway… that would work to my advantage.

I need to clear my head some more (installed a 7 foot ceiling fan in the shop today - that helped) and then sit down and come up with the most practical / functional solution.

 

[Darren]

I need to install some fans myself. I haven't looked into it too much, but a 7 footer would help a lot!

 

[RobinHood]

It was a good thing I took a break from the mill issue this morning.

Went back to look at that sprocket and it’s key way again. Turns out the one end is not welded after all. It was CI powder hard packed into the slot. Most likely from the pulley wearing and rocking on the shaft. It took a small chisel to get the stuff out. The “discolouration” was not from heat but rather some chemical staining; someone used some funky grease on the lead screw - which is right above it - and some probably dripped down. This stuff is nasty: it stains everything it touches reddish - blueish and floats like a veil in the parts washer liquid. Never seen anything like it before.

So, that is good news as we are back to the original solution of making the pulley have two bosses sticking out: an OE length one on the outboard side and stubby one on the inboard side and shortening the sprocket body to match.

I shortened the sprocket body to 51 mm (from original 57 mm). This gives me about 7 mm (~1/4 in) of good shaft on the inboard side of the damaged area. Took a light skim cut off the front face and then removed the bulk from the rear. Left 0.15 mm to finish the faces off on the surface grinder. Could have done it all on the lathe, but why not use the grinder? Perfect job for it. Gets both faces flat and parallel to each other.



Next will be the new pulley bushing.

 

[Darren]

Nice work. Good thing it wasn't some ungodly hard material.

 

[RobinHood]

Bored out the pulley for the new hub. Decided to make a little step to push the bush up against. Planning on heating up the pulley in the BBQ to about 150*C. It should expand enough for the 0.05 mm press fit I have the bushing oversized to. I’ll also put red locktite on it.



The bore of the bushing was made to the same 25.02 mm as the ground bore of the sprocket that sits on the same shaft behind it. It is a nice sliding fit to the shaft, but I should have stopped at 25.00 mm for an even tighter sliding fit.

Here is the bushing before parting off.



Next is getting the key way into the 25 mm bore. That is going to be tricky as the bore is 85 mm deep.

I have two 1/4” broaches; one is a Dumont and the other is an Import. I’ll probably take the Import one and surface grind it down to 6 mm. Then I need to make a 3.5” long broach bushing for the bore. Hopefully I’ll be able to push the broach through this very long bore…

 

[DavidR8]

Darn fine work there!!

 

[RobinHood]

Now I own a 6 mm broach (ground down the extra 1/4” broach I had)…

Indicating it parallel to the wheel travel


Grinding the second side


And the finished broach.


Took a bit of a risk by measuring from both sides of the body down onto the teeth flanks. It was the easiest I could figure how to measure my grinding progress.

The broach body was surprisingly uniform, flat and parallel at 0.380” thick. That gave an original step down onto the teeth flanks of 0.065” per side for the original tooth width of 0.250”. In order to get to the new 6.0 mm tooth width, that step down needed to be 0.0719” per side. Since the body was flat and parallel, I could just use a depth mike to measure the step without removing the work piece from the mag chuck. That worked great. Ended up with a final tooth width of 6.01 mm. It fits perfectly into the OE sprocket’s keyway. I call that good enough for me.

 

[RobinHood]

Repair is done.

The broach worked like a charm. Here you can see the chips it cut after the first pass (the second & third were the same).



Used my 4 ton bench top press (don’t have an arbour press). Here is the third pass.


86 mm long, 6 mm wide keyway after broaching.


Hub heat shrunk into the pulley - hence the discolouration of the hub. Front and rear hub faces were surface ground after; that’s why they are shiny. The two pins engage in the hand wheel (which needs to be made or purchased).


And for good measure there are two set screws at the interface line of the new hub to the parent CI pulley.


The assembly fits nicely onto the shaft with no play and minimal runout. I also made two new keys from 1/4” stock - ground it down to 6 mm nominal on the surface grinder.

 

[Darren]

Nice work Robin!

 

[140mower]

Looks like a very nice repair. Well done.

 

[Brent H]

Bravo old boy!! Well done! Well done indeed!!! Clap clap clap !!!!

Great repair! Nice work!

 

[DavidR8]

Awesome work @RobinHood

 

[PeterT]

That sure is a clean keyway cut & nice retrofit. Back in business!

 

[6.5 Fan]

Some nice work, congrats on a job well done.

 

[Susquatch]

Used my 4 ton bench top press (don’t have an arbour press). Here is the third pass.

Very nice work @RobinHood!

It's not obvious to me how you used your bench press to do this. I've stayed away from broaching because I assumed that special (expensive) equipment was required. I'd like to know a bit more about the process you used. Can you explain this step a bit more to a novice at broaching?

 

[RobinHood]

The bench press was the “muscle“ to push the broach through the bore. On a long keyway like this, there are many cutting edges engaged at the same time ==> lots of axial force required. An arbour press of sufficient size - both in the force it can exert and the headroom needed to start the broach - would work also. I don’t have such an arbour press.

Do you understand how a broach works? If not, I can try and explain it to you.

 

[RobinHood]

Yes, broaching usually produces a very nice result. I found that the broach guide needs to fit very well to the bore and the broach itself. Both need to be close sliding fits. Surprisingly, my second (offshore) broach set also had the guides cylindrically ground like the Dumont set.

I could not use the standard guides for two reasons:
a) this is a 25mm bore; I only have SAE broach sets (hence also the broach width mod to 6mm above)
b) standard guides are nominally shorter that what I needed

So I had to make my own guide bushing & backers to fit the 25mm bore nicely and be at least 86mm long. I did not spend the time to OD grind the bushing as I got a good enough fit and finish by just turning it.

L to R: OE backer & 1” guide bushing; custom bush; 2 backers, 25 x 86 mm bushing, modified broach; custom bushing


If one attempts to use a guide & backers that are shorter than the depth of the bore, there is a near 100% chance that you will break or bend the broach. In super soft material (plastics, and maybe aluminum), one can get away with guides & backers a little shorter than the bore because the cutting forces are much lower. But in steel, I always just spend the time to make the correct length of tooling. They are not lost, one can always us a guide that is too long in a shorter bore, but not recommended the other way around.

 

[Tom O]

I was told in the distant past to not push it through in one go but to press in stages in case alignment problems snaps the broach

 

[Susquatch]

Yes, broaching usually produces a very nice result. I found that the broach guide needs to fit very well to the bore and the broach itself. Both need to be close sliding fits. Surprisingly, my second (offshore) broach set also had the guides cylindrically ground like the Dumont set.

I could not use the standard guides for two reasons:
a) this is a 25mm bore; I only have SAE broach sets (hence also the broach width mod to 6mm above)
b) standard guides are nominally shorter that what I needed

So I had to make my own guide bushing & backers to fit the 25mm bore nicely and be at least 86mm long. I did not spend the time to OD grind the bushing as I got a good enough fit and finish by just turning it.

L to R: OE backer & 1” guide bushing; custom bush; 2 backers, 25 x 86 mm bushing, modified broach; custom bushing
View attachment 22403

If one attempts to use a guide & backers that are shorter than the depth of the bore, there is a near 100% chance that you will break or bend the broach. In super soft material (plastics, and maybe aluminum), one can get away with guides & backers a little shorter than the bore because the cutting forces are much lower. But in steel, I always just spend the time to make the correct length of tooling. They are not lost, one can always us a guide that is too long in a shorter bore, but not recommended the other way around.

I see. Thank you! I had thought the broach was held solid by a broaching tool holder. I didn't realize a guide inside the part was used. That pretty much clears up my confusion.

 

[RobinHood]

I was told in the distant past to not push it through in one go but to press in stages in case alignment problems snaps the broach

That sounds about right. With the hand pump, the broach moves in small stages. I‘d push it about 1/2” to 1” and then back off the ram. Re-center / align everything and push some more. Worked very well, albeit slowly.