Sunday, November 4, 2012

Metalworking: Slitting Saw Arbor

Okay, so this is not an electronics project, but it is my blog, and lately I've been spending my hobby time doing metalworking projects at Xerocraft, Tucson's local Hackerspace.

We have a old Logan Lathe and a generic chinese Mill Drill that I've been using primarily to make tooling for the lathe and mill.

Its been a lot of fun reviving the love of machining that I learned from my middle school (called Jr High back then) metal shop class.

This project was to build a bushings that allow our R8 shell mill holder to be used for 1" arbor hole slitting saws (like the one on the picture above), or other side milling cutters.

There were two parts needed to use the arbor for slitting saws.  Both started as a 1-5/8" diameter 1117 free machining steel rod.

The main bushing started as a solid piece of steel.  I mounted it in the three jaw chuck on the lathe and faced both sides square and flat.

Next I center drilled it and drilled progressively large holes through the center in 1/8 increments starting with 1/4" and ending with this 7/8" reduced shank (aka Silver and Deming) bit.

Next I set up a boring tool in the boring bar toolholder I made on the mill, and bored the remaining 1/8" to get the hole to fit the tool with a very close fit.  I did this by first boring to .995", then test-fit and bored a few mils more until I got the desired fit.

The next step was to coat it with blue dye and mark it for milling.  I carefully mounted it in the vice properly aligned so I could mill it directly down the center line for the alignment slots that keep it from turning on the arbor under the milling forces.  This required some careful setup, but was a it easy milling operation.  I actually broke a endmill while milling this.  The slotting operation in steel makes for a much heavier chipload that could not effectively clear out of slot.  If you look closely at the picture above, you can see the very fine chips caused by the cutter cutting its own chips over and over instead of clearing them out of the slot.

I cut the slot a bit too deep and used the lathe to adjust the depth of the slot by facing off the excess material.  Next I turned it around and faced the other size to get the length exactly right.  That finished the first piece.

The second piece was done entirely on the lathe.  First I mounted a small piece of the same 1-5/8" rod in the three jaw chuck and faced one side flat and square.   I drilled a clearance hole for a 3/8" drill.  Again with the same facing tool, I faced out a notch so the part fit perfectly into the top of the bushing.

Next I flipped the piece around and used a different tool to face out an indentation starting at the center hole to fit perfectly over the top of the arbor.

The two pieces fit together in two different ways depending on the width of the slitting or slotting saw used.  If a thin slitting saw such as the one in the picture below is used, the concave side is used so the saw is held tightly on the arbor.  If a thicker saw is used, the convex side is used to give support of the top on the bottom from the arbor, and on top from the machined piece.

The whole part goes together as shown below.

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