Metal Selection

[epicfail48]

Hoping to pull some wisdom from the hive mind, im looking for a pre-hardened stainless thats relatively easy to machine and wont break the bank. Project in mind is this:


A bolt-action pen. Stainless im wanting to keep rust at bay (duh), and prehardened i want for longevity and scratch resistance. Now, hardened is complete overkill, i know, this is more of a "meh, why not" thing for me. The one pictured is 416 stainless, which turned out really nice, but i had some issues with it. For one is the price, its a delight to work with, but the price for 416 is a little high for my taste, and getting it pre-hard just drives that up further. I can harden the pieces myself and buy annealled for slightly cheaper, but then i have to factor in the heat treatment cost. Im also not in love with the finish i can get off the tool, seems like no matter what i do the surface always ends up kinda fuzzy. Carbide, HSS, aluminium and steel specific inserts, pre- and post-heat treat, nothing worked. Easy enough to clean up the finish with some sandpaper, but still, if i can get it looking good off the tool thats less work for me.

Ive made these from 304 stainless before, and theyve turned out just fine, i just want to push the envelope as it was. I thought about 4140ph, but id be dropping the stainless requirement. Getting some 4140 and rust-bluing it is on the project list, but id still like to have a stainless in the book of tricks. The current favored option is 17-4ph, its relatively inexpensive in the pre-hard state and ive heard its horrible to work with, about the same machinability as 304. If anybody has any recommendations, please and thank you!

[MattiJ]

17-4 H1150 probably your best bet.
I have same experience about hazy surface on 416, I think its due to sulfur content. You can get "shiny finish" but it takes awful high sfpm on finishing pass and insert life is less than stellar.

Price-vise prehard 416 and 17-4 are about same price on mcMaster, dunno where you buy and what you pay. (about 15usd per feet)

[lynnl]

"...horrible to work with.."? ...17-4? Hogwash!

I've not done a lot, but I've found the 17-4 pre-hard a delight to machine.

[shampine1]

I agree, 17-4 machines a lot better than 316 type stuff. Much less gummy.

Sent from my SAMSUNG-SM-G891A using Tapatalk

[MattiJ]

I agree, 17-4 machines a lot better than 316 type stuff. Much less gummy.

Sent from my SAMSUNG-SM-G891A using Tapatalk

Maybe OP was mixing the hardened 17-4 to soft annealed 17-4.

[Bob La Londe]

I did several of them for Christmas presents in 2017. I just used 304. 304 is a bit of a pain to machine, but by using sharp drills and cutters and pushing hard I was able to get it done. I started out to make a dozen blanks and finished ten pens. The two I destroyed were because of trusting factory fresh grinds on more expensive drills. After regrinding them I almost couldn't push fast enough.

If I do it again I'll probably order some 416. Cheaper and stronger, and machines a little nicer. There is nothing wrong with the 304 pens. They seem to have held up just fine and they are plenty strong, but 416 really does seem to machine easier.

And... I am thinking about doing it again. I've been bouncing around the idea of making a double action version with a regular space pen refill in the bottom and a carbide scribe in the top with a stronger than click pen spring on that side to prevent accidental stabbings.

I just used a cross tapped socket head screw for the activation stud on the original, and it might double as a set screw to lock in the carbide scribe for the double action version.

I would suggest drilling to just under final dimension of the cap section before slotting the bolt slot, and then using a spiral flute reamer to take it to final dimension to remove the interior burr. That was the second hardest part. Removing the burr. The hardest part was working up the nerve to drill the hole for the roller tip. I would up using a carbide drill for that at a pretty high speed.

[Toolguy]

Might look into 420 SS. That is used a lot for making plastic injection molds.

[Doozer]

You might want to design your pen to use stainless
tubing and machine the ends to press fit or what not.
That would save cost over solid bar.

-D

[Bob La Londe]

Tube tends to cost more than rod, and there is a wider range of rod diameters from many vendors. It would be a trade off I think between saved labor vs saved material cost.

[MattiJ]

Tube tends to cost more than rod, and there is a wider range of rod diameters from many vendors. It would be a trade off I think between saved labor vs saved material cost.

About same price for 304 and 316 stainless tube and rod (tube actually a bit cheaper around here) but good luck finding inexpensive source for 416 or 17-4 tube!
My free supply of 416 is from gun shop so it comes in thick wall and short pieces

[Yondering]

17-4 is definitely not "horrible" to work with, either annealed or hardened. If you're using a good sharp tool, it leaves an excellent surface finish and isn't any harder to cut than a lot of other steels. In annealed condition it can be hard to get chips to break with shallow cuts, so you have to deal with the swarf, but that's the only "issue" I've encountered. I really enjoy turning 17-4 PH myself, in either condition.

[epicfail48]

Seems like thats a lot of votes for the 17-4ph. To be clear though, i did say based on numbers is seems to be not horrible to work with. Never worked with it myself, so i have no idea how well it works, the only thing i can go off is anecdotal evidence and the machinability charts that put 17-4 a few points higher than 304. Even then though, minus the work-hardening that tripped me up the first time working with 304 ive not had much issue with it, im just spoiled after finding out just how much better the 416 is. If it werent for that blasted finish and the cost...

As far as the cost goes for these, im buying 1/2" to have some to turn down to final dimension. Going through McMaster, 416 prehard is $24.60 for a 1 ft length, and 17-4ph is $13.65, which is why the 17-4 was so appealing to me. If i can pay just over half the price, im a lot happier

[PStechPaul]

JFF I checked AliExpress. They have various lots of SS rod:

https://www.aliexpress.com/item/SS30...351914190.html (2 pieces 10mm x 500mm SS304, $34 including shipping.

https://www.aliexpress.com/item/304-...954889647.html (1 piece 14mm x 200mm SS305 $54 including shipping)

https://www.aliexpress.com/item/New-...694851185.html (stainless steel pen $0.50 each free shipping)

https://www.aliexpress.com/item/1pc-...818051617.html (1/4" SS304 pipe, 200mm long, 0.54" OD, 0.364" ID, $4 each, free shipping)