what to do with a free scrap dumpster find ?

decided to try a different material this time around, the first one i made from 4140HT but this one i am trying 1144SP because it machines better and is close to the same material. typically something very hard and heat treated would be used but for a home built spindle this a good choice and should do ok, the yield strength is actually a little bit better @ 100,000 psi the 4140HT is around 95,000 psi but it is slightly harder. they are both hard materials but i will soon find out first hand which i like better

steel choices are like Linux CNC to many damn choices

I did not see anything about that process when picking material. the only surface treatment i seen was this material can be carburized. as is it sits in it's current form it falls somewhere around 25 to 28 on a Rockwell C scale. it's tough material and most of the uses for it are when you want to do away with the heat treating process but still need something tough. on a #30 tapper the pull forces need to be in the 900 to 1200lbs of force range. once you go to a #40 tapper that jumps to about 2200lbs of force and when you get into a #50 tapper you are looking at close to 5000lbs of pull force.

right now with a 3 hp limit and a #30 tapper i think it should be fine as is. the yield strength is 100,000 psi plus in it's current state. i agree there are options to make it stronger i think i would rather sink any extra money in making it more accurate by getting better bearings. i found a set of two NSK 7009 angular contact P4 or ABEC7 class for $165 i still need to look around for two more deep groove bearings for the drive side.

$90 for a piece of material $200 for bearings and $40 for bearing locknuts adds up quick to get costly machine might have been free but the cost of parts adds up quick

i did look at that site and i did not see 1144SP listed so it might not be something that can be treated that way? 1144SP and 4140 are about 99% identical in make up. the only thing i seen as being a main difference was the high sulfur content of 1144 which makes it not very weldable which is not even a factor for my use. i had a chance to rough the shaft out over the weekend and it is actually different to work with. it cuts better at high feed rates than going slower. it is a little bit easier on carbide but still dulls an insert pretty quickly. and it cuts better dry than with my favorite go to with no flood coolant the can of WD-40 maybe a mist that is water based might work too? weird it cut better dry though

from what i could gather this process does not have to much impact on sizes to a point but when you get into tenths it can change sizes. so with bearing fits and the spindle tapper you are into those kinds of tolerances. so your back to square one. the best plan would probably be size the not important sized features and leave .015 on the bearing diameters and stock in the tapper to grind in with a tool post grinder. the tapper could be done with a make shift set up with a mounted wheel. then send it out to get carburized. the depth of surface treatment is much deeper with carburization. somewhere around .06 to .08 for a depth from what i gathered in a quick look through. carburizing would land you well into 60's on a Rockwell C scale.

but i just spent well over $200 for spindle bearing and i was broke before that soo.....

the way i did my draw bar is pretty close to zero contact other than where the air cylinder will make contact to eject the tool. i went with a high strength die spring rather than spring washers. seemed like a more compact holder tension. anything beyond a #30 tapper would not work because the die springs would be hard to find or fit. all the clamping happens when the fingers get drawn into the smaller diameter on the ID of the spindle the ejection happens when the stoke of the draw bar is if forced down the ID into the large section of the ID bore. the preload on the draw bar is done by compressing the spring with a nut on the topside, most likely two with the second acting as a locknut to hold the spring tension. i wanted to do something adjustable so i could get the most out of a 100mm bore air cylinder. the one i have will do a little over 1200lbs at 100psi and can go up to 145 psi max. i don't know exactly how much i can get out of my compressor beyond 100psi the shut off is 120psi. it's not a small compressor but it's only single stage with a 6.5hp motor and a 60 gallon tank.