Repurposing an old lathe into a dedicated slotting machine

Atlas / Craftsman 6 inch Metal Lathe

I am not really sure how old this lathe is - apparently Atlas began manufacturing this model 1936. The serial number stamped on the bed is 24117.

I recently came across this old lathe when cleaning out my fathers shop after he passed away. It was pretty small for most of my metal lathe projects - but I quickly realized that I could create a dedicated fixture with it, and only have to put forth a little money in parts and invest a little time.

I often use tab style dropouts for front and rear dropouts. Up until now I have been slotting the chain stays, seat stays and fork blades to accept these slotted dropouts by hand. Hacksaw and file. Its not exactly difficult, but it takes time - especially if I want to put the slot in at an angle as opposed to right down the middle of the stay.

I decided to put a arbor and a slotting saw in the chuck and convert the tool holder / rest into a clamp to hold the stay.

The lathe has a backgear - which significantly slows down the rpms and ups the torque. According to the manual I can attain a rpm of 54 by utilizing the backgear. This will help me maintain the SFM / cutting speed of a 3 inch slotting saw which will be required to make appropriate slots in stay / fork blades.

My research yields:

SFM = 0.262 x D x RPM

SFM = 0.262 x 3 x 54

SFM = 43 Feet Per Minute

Further research yields 65 SFM for Heat Treated 4130 and 120 SFM listed for regular 4130. So this should work great on Heat Treated 4130 stays / fork blades - As long as I keep the feed rate really slow and steady.

Here is a picture of it in action.

Basically - the setup requires a modified a v-block, and a T-Nut to hold the stay on the tool rest. as you can see from the picture - I clamp the stay as close as possible to minimize vibrations.

Here is a picture of a test slot I made - it came out pretty nice. Looking forward to using it for the next bicycle in the queue.