Drilling through tool steel?

[rickpaulos]

I need to make a new pin for my garden shredder/chipper. The parts diagram calls the part a pin so that's the term I'm using. Round rod or shaft or axle.

The pins are 8 & 11/16" x 1/2" with one hole drilled for a 3/16" spring dowel pin.

I previously (2015) broke a pin at the spring dowel pin hole. I bent another yesterday when the spring dowl pin fell out and the pin slid out of one end of its holder.

two questions.

How can I tell what grade of steel was used for the pin? I believe it is harder than just mild carbon steel.

And how hard is it to drill a hole for the spring pin? I don't have a drill press, just electric hand drills and a bench vise.

 

[GRB]

If it is an axle on a tool like that where the wheel is held on by a spring pin, it is mild steel.

Drill it with a 135 degree split point drill with no problem. Otherwise center punch it very well and start with a small drill bit and you should be fine.

 

[KBigg]

If you can cut it with a standard file you'll be able to drill it just fine with a high speed drill bit. There's no way of telling what kind of steel it is though. The only thing you can test is the hardness with either a set of hardness testing files or a Rockwell tester. For drilling a hole by hand in a round part just make sure you center punch it deep and use a vice to hold the part.

 

[MattT]

How can I tell what grade of steel was used for the pin? I believe it is harder than just mild carbon steel.

You aren't going to be able to tell exactly what grade it is. You can get a rough idea by trying to file it. If it doesn't cut as easily as mild steel then it'll be a stronger/tougher steel. If the file skates across it then it'll be case hardened. If it's mild or something tougher you'll be able to drill it with good quality HSS bits. Hardened your best just buying a new pin unless they're NLA.

And how hard is it to drill a hole for the spring pin? I don't have a drill press, just electric hand drills and a bench vise.

If the hole has to line up with a hole in another part your only chance of getting it close enough is to clamp the parts together and use the hole to guide the drill.

If not then file a small flat on the shaft for the drill to start on. Then center punch and try it. How well it comes out is all down to how good you are at eyeballing square and centered. Good luck.

 

[2oolhound]

How can I tell what grade of steel was used for the pin? I believe it is harder than just mild carbon steel.

Google "spark testing steel" to find charts to compare with your results. Do it in a dark room.

 

[kazlx]

Where does the pin go? It's almost certainly plain 1018 if it has a cross drilled hole, isn't ground and doesn't have any sort of precision fit.

 

[matt_i]

If you want "better than 1018" my goto is W1 drill rod which is used in the annealed state (no heat treatment). It also has the benefit of a nice ground finish and doesn't cost like mad unless you get above 5/8" or so. Can be purchased in 3ft or 6ft lengths so easy to ship for your 8.813" length.

The hard part about drilling the center of a shaft is the fact that the drill bit wants to slip off. The suggestion to file a small flat and center punch it is a good one. In a mill I'd use a spot drill and an edge finder to find the center of the shaft. But eyeball works well too. Drill on-size for the spring roll pin.

 

[rickpaulos]

Pictures:

The first shaft broke in 2015 right were the hole was drilled. That was exciting. First run for cover, then run back over to shut the motor off before something bad happened.


The second shaft got bent Sunday when the spring pin fell out, the shaft shifted to one side enough so it wasn't supported on one end. It's normally supported at each end and near the middle.


Having a hole and spring pin just doesn't seem like the best design. And you can see the spacers are getting beat up by the harder flails. Those spacers are about 7/128" thick.
Now I'm thinking of NO hole in the shafts, use either a pair of solid collars with set screws or a pair of split collars to hold the shaft centered. And use a bunch of extra wide hardened washers to fill the gaps so the rotating flails stay put. Washers would give me more flexibility in spacing the flails in alternating patterns on each shaft. I'll need to use the same hardware on all four shafts to keep the cylinder that spins at high speed balanced. If a split collar came apart, I'd have shrapnel coming out at bullet speeds. I think the solid collars would not break apart if a set screw came out but I'm not a fan of set screws where there is no key way (Another weak point). Being able to remove everything is needed to periodically rotate the flails to get to a new cutting edge. Installing and removing the spring pins is quite annoying as the access is limited and the cylinder wants to move. The flails must be free to rotate on the shafts. Using all washers for spacers would add some rotating weight. But maybe not that much more than the models that came with the outer sleeves.* Acceleration to top speed would be slower but more rotating mass may help it keep it's speed.

Solid collars with set screws:


Split collars with 2 cap head screws:


Extra thick washers:


Really Extra Thick washers 7/32" thick.


original Parts diagram:


*Looking closely at the diagram, there are "Outer Sleeves" that my shredder did not have. I'm thinking those are to help keep the flails perpendicular to the shafts. The diagram does include several models.

I did read up on spark testing. Interesting topic. The bent shaft sparks were very dense, orange and sparkely at the ends. The spacers not so much.

rick

 

[ant.foste]

So Rick while on this topic, how well does your machine work (prior to failure) for limbs? I'm interested in buying a small wood chipper, but the Chinese equipment on the market has made it difficult to view any online review as an honest one. First hand accounts are rare. It seems you like this unit enough to keep repairing it.