QCTP adapter

[Gary]

I have started a project of turning an adapter that will fit over the QCTP mounting bolt. Fairly straight forward and should be easy enough to make even with my limited skills. Here's a problem I encountered: I need to drill a center hole of approx. .550" and whatever the steel happens to be, it's super hard to drill. The round I'm using used to be a wrist pin on a JD tractor/excavator. It's 2" x 3". It cuts fairly easily on the lathe but drilling is a total other thing. I started by center drilling and followed with a 1/4" drill bit. No go, and this drill bit is new. Any suggestions?

 

[wquiles]

I have started a project of turning an adapter that will fit over the QCTP mounting bolt. Fairly straight forward and should be easy enough to make even with my limited skills. Here's a problem I encountered: I need to drill a center hole of approx. .550" and whatever the steel happens to be, it's super hard to drill. The round I'm using used to be a wrist pin on a JD tractor/excavator. It's 2" x 3". It cuts fairly easily on the lathe but drilling is a total other thing. I started by center drilling and followed with a 1/4" drill bit. No go, and this drill bit is new. Any suggestions?

Gary,

I know you said it is steel, but I have seen the same exact problem every time I drill Titanium, when I as making DE Titanum handles. My "solution" was to use a slower speed (I think about 225 rpm's on the lathe), heavy lubrication, heavy and consistent pressure (to prevent work hardening), AND had to use a carbide drill bits - regular and HSS bits couldn't do it.

Will

 

[fiver]

it could be improved plow steel too.
slow speed and cutting oil, the taper on the bit face can make a difference too.

 

[Brad]

Will may well be onto something. It could be that you aren’t pushing the bit hard enough and are getting workhardeing.

 

[KeithB]

Or it could be a quench hardened steel that needs annealing to be easily machinable. Don't know how hard you need it to be but it isn't all that hard to anneal small pieces. Course that will cause some scaling and will screw up the surfaces you already have done. If you HAD to turn it using carbide you will probably need to drill it with carbide.

 

[Gary]

Turns pretty easy, but I do use carbide tipped tools.

 

[Brad]

Turned easily with carbide tools doesn’t mean much unless you use carbide drills.
I bet that thing is pretty hard.

 

[KeithB]

Wrist pins are usually hardened, either through hardened or just case/surface hardened. If they are through hardened they are probably 4130. 4140, 4340, or 1050. If they are just case hardened they could be anything from 1018, 1020 or 8620. (Rough rule of thumb: Take the last two digits in the steel code designation and put a decimal point in front of it. If it is greater than .25 then it has enough carbon to through harden by quenching. If less than .25 then you have to add carbon from the outside through the surface to case harden it.)

It may be case hardened and you've cut through the hard surface on the OD but the surface on the end of the piece is still hard. Did you machine the end face? If it is case hardened it can be softened with a oxyacetylene fine tip welding torch just in the center where you are drilling. Maybe once you get through the outside it might go easier. Maybe.

 

[Gary]

Thanks Keith. I think this old wrist pin is case hardened steel and not Titanium. I did face the piece and tomorrow I'm going to turn the piece around and face the other end. The other end is where the pin was cut in half and I will be able to tell more about the case hardening.

 

[smokeywolf]

If you HAD to turn it using carbide you will probably need to drill it with carbide.

This ^^^^^

 

[Gary]

Turned the piece end for end and commenced to drill; drilled a pilot with a centering drill; then sharpened a 1/4" drill and with lots of force was able to drill through. I have a number of fractional bits and got up through 1/2". It actually drilled fairly easily once I got the initial hole established. Now to find a 33/64" bit.

 

[wquiles]

Great update Gary. Looks like the sharp drill and extra force was the key in this case

 

[KeithB]

The problem with most twist drills is the center of the drill doesn't cut the material, it pushes/extrudes the material sideways where it does get cut by the cutting edges. If you can get a drill with the point thinned properly so it cuts virtually from the center on out it works best for hard materials. Hard materials by definition don't/won't extrude very well. That's one reason for using a pilot drill, so the next size drill doesn't have to push any material out of the center. Most twist drills are ground to have the flutes get smaller and the center get larger the closer you get to the shank, so thinning the web gets even more important as the drill gets resharpened.

 

[smokeywolf]

Great point Keith (no pun intended). One of the reasons split-point drills are a good choice for hard to drill materials.

 

[Gary]

Got a couple of hours in the shop this afternoon and did some shaping. I have to do some clean up for a bolt head tolerance and I'm going to be able to try it out. Tomorrow I'm going to buy a 9/16" bit and finish this project Mine is fabricobbled to be a one off specifically for my vise.
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Finished pic on the right setting on the top slide.