Spring Gun design/machine shop project

[Scotchmo]

I finished the most complicated mill part today. The front plugs for the lower receivers. My mill/drill has .023 and .014 inches of backlash in table dials. I lose track of it sometimes and am lucky to hold .02 tolerance at times. This would be an ideal part for CNC. But I would be happy with ball lead screws or a digital readout.



This part houses the anti-beartrap and safety interlock mechanism. Not very exiting but necesary on a sliding breech spring gun. On my TF58, you need three hands in order to override the interlock and uncock the rifle. I compromised a little on this design. I did not try and make it idiot proof because I wanted to be able to safely uncock it if needed. The automatic safety does not go on until you disengage the anti-beartrap. So if you you want to uncock it, you pull the lever back to engage the anti-beartrap, release the safety and then pull the trigger. The anti-beartrap will catch the compression chamber and then you can hold the lever, release the anti-beartrap, and return the lever to the closed, uncocked positiion. At least that is the intent.

I made a 1-3/16-16 tap for the stock tube. I made it slightly undersized for a tight fit. I case hardened it. It was good practice for case hardening the sear ring that will go on the piston. The tap cut a decent thread in a test piece but it was too tight. I may just buy this one since it has to fit a standard AR15/M4 buffer tube. I may still make the tap for the compression chamber since I am also making the cap/plug so I can adjust the thread fit easily. The heating, case hardening and quenching seemed to take some of the edge off of the cutting edge on the homemade tap. It still cut OK. If you are only going to use it a couple of times in aluminum, you can probably forgo the case hardening.




 

[Donny]

man reading Scotchmo and Bob posts make me feel stupid

[rsterne]

Well you qualify as the first person I have seen make a custom TAP.... Well done....

Bob

[ZipSnipe]

great job on the tap , guess you didn't want to try internal threading on the lathe?

[QVTom]

Wow!  Seems a bit crazy but results are what count.  I am curious why you would not attempt a single point internal thread first?  How much muscle does it take to start that thread with the full profile lead?  I bet you got a workout!  When I need a custom tap I just get out my check book

Nice progress and nice work!

Tom

[Scotchmo]

great job on the tap , guess you didn't want to try internal threading on the lathe?

I have never cut an internal thread on a lathe but I did want to try it. I set the lathe up to do it to see if it was possible. The upper receiver tube that I will be threading is 24 inches long and 1-1/4 inch OD. My headstock will pass a little under an inch only. So I needed to hang the tube out and use a steady rest. My lathe bed is 4 feet total length. I had to remove the tail-stock and crank the carriage all the way to the end of the bed. If I went out far enough to get the tool into the tube, the thread dial would not engage since it hit the lead screw support. I would have to rig up an unconventional tool holder that extended to the right off of the carriage and curved back but it seemed easier to make a tap. I could do it on the short compression chamber but I don't want a thread relief on it, so it gets a tap too.

Wow!  Seems a bit crazy but results are what count.  I am curious why you would not attempt a single point internal thread first?  How much muscle does it take to start that thread with the full profile lead?  I bet you got a workout!  When I need a custom tap I just get out my check book

Nice progress and nice work!

Tom

It took some muscle. But it cut smooth with no hangups. I'm poor (or cheap). Just for the two taps and large end mills that I would need would be about $250. So I made do. I'm going to give the receiver tap another go. And hopefully get the fit right this time.

I'm a little envious of your milling equipment and skills.

[MichaelM]

instead of running the threads under power on the lathe you can make you a removable crank that attaches to the rear of the headstock so that when you want to thread you can just attach the crank handle set your compound and select the right gears for your thread.... then you just set your halfnut andstart cranking when you get to the end of your thread you back the compound off a tad reverse crank the handle till your carriadge is back to the beginning run the coupound back in and start cranking again...... basicaly everything you would do under power but your doing it manual and you NEVER disengage your half nuts so you never loose your index with the thread your cutting..... and no need for the threading dial..

super simple to make a crank too... just get you some scrap roundstock (delrin alu steel doesnt matter) drill you a hole the length of it, then turn it to just under the size of your headstock bore, then cut the pipe at a angle in the middle.. Get you another peice of scrap round square whatever you got make you a crank arm and handle then take a long bolt and bolt the whole thing together with the tube angles mated together... slide the whole thing into the bore of the headstck tighten the long bolt down and the angled ends try to slide past each other and grip the inside of the bore(Kinda like an old gooseneck on a bike would stay down into the forks) .... you now have a removable crank

kinda like this except they have a collet shown attached at awell
http://homepage.mac.com/bhagenbuch/machine/pages/spindlecrank.html

just remember to REMOVE the crank before ou power back up!!!!!

[Scotchmo]

instead of running the threads under power on the lathe you can make you a removable crank that attaches to the rear of the headstock so that when you want to thread you can just attach the crank handle set your compound and select the right gears for your thread.... then you just set your halfnut andstart cranking when you get to the end of your thread you back the compound off a tad reverse crank the handle till your carriadge is back to the beginning run the coupound back in and start cranking again...... basicaly everything you would do under power but your doing it manual and you NEVER disengage your half nuts so you never loose your index with the thread your cutting..... and no need for the threading dial..

...

That is a good idea. I'll have to try it. The other good thing about your method is that I don't have to incorporate any thread relief.

I won't need a crank. My lathe is 84 years old. It is a transitional model from when they were switching from line-shafts to self contained units. When I want to run it manually, I just keep tugging down on the drive belt.

This lathe is old but the ways are nearly perfect. I think it was retired before WW2 so it escaped the heavy use that the newer lathes got.

[QVTom]

It has been a while since I have made a  thread on a manual lathe but I do remember the process quite clearly.  I prefer not to have an undercut on an ID thread and would use the cross slide to back the tool out of the cut on the last couple of revolutions.  I would uses a dial indicator and a mighty magnet on the carriage travel to determine when to start the cross slide back out. Once the tool is clear of the thread, disengage the half-nut, back up the carriage, run you cross slide back in to 0, make the depth adjustment on the compound slide and make another pass. I prefer to do the threads under power to avoid jerkiness in the peripheral speed of the cutting tool to get the best surface finish possible.

I can see where the crank method would be invaluable on a blind bore where a slight hesitation would be disastrous!


Tom
 

[Pete]

instead of running the threads under power on the lathe you can make you a removable crank that attaches to the rear of the headstock so that when you want to thread you can just attach the crank handle set your compound and select the right gears for your thread.... then you just set your halfnut andstart cranking when you get to the end of your thread you back the compound off a tad reverse crank the handle till your carriadge is back to the beginning run the coupound back in and start cranking again...... basicaly everything you would do under power but your doing it manual and you NEVER disengage your half nuts so you never loose your index with the thread your cutting..... and no need for the threading dial..

super simple to make a crank too... just get you some scrap roundstock (delrin alu steel doesnt matter) drill you a hole the length of it, then turn it to just under the size of your headstock bore, then cut the pipe at a angle in the middle.. Get you another peice of scrap round square whatever you got make you a crank arm and handle then take a long bolt and bolt the whole thing together with the tube angles mated together... slide the whole thing into the bore of the headstck tighten the long bolt down and the angled ends try to slide past each other and grip the inside of the bore(Kinda like an old gooseneck on a bike would stay down into the forks) .... you now have a removable crank

kinda like this except they have a collet shown attached at awell
http://homepage.mac.com/bhagenbuch/machine/pages/spindlecrank.html

just remember to REMOVE the crank before ou power back up!!!!!

Well knock me over with a feather..I have heard it all now...
toss the crank handle away... peddles man peddles  and a seat...

But all jokes aside it could be useful on some threads.
small threads in a blined hole or against a shoulder..

[MichaelM]

instead of running the threads under power on the lathe you can make you a removable crank that attaches to the rear of the headstock so that when you want to thread you can just attach the crank handle set your compound and select the right gears for your thread.... then you just set your halfnut andstart cranking when you get to the end of your thread you back the compound off a tad reverse crank the handle till your carriadge is back to the beginning run the coupound back in and start cranking again...... basicaly everything you would do under power but your doing it manual and you NEVER disengage your half nuts so you never loose your index with the thread your cutting..... and no need for the threading dial..

...

That is a good idea. I'll have to try it. The other good thing about your method is that I don't have to incorporate any thread relief.

I won't need a crank. My lathe is 84 years old. It is a transitional model from when they were switching from line-shafts to self contained units. When I want to run it manually, I just keep tugging down on the drive belt.

This lathe is old but the ways are nearly perfect. I think it was retired before WW2 so it escaped the heavy use that the newer lathes got.

That sir is a darn pretty old lathe.... very nice looking *(&^ I would trade out my 9x20 for a lathe like that anyday

[Scotchmo]

Update on my progress:

The lower receivers are almost done. I specified stainless steel on many of the small parts but I don't have much SS material and did not want to order any for small items. In some instances I just used what was in the shop. Usually mild steel. For the safety interlock, I cut up a bicycle fender bracket:



The next picture show the guts of the lower receivers of rifle A and rifle B (I'm building two):



The next picture shows the guts of one rifle with the anti-beartrap catch up:



The next picture show the release button pushed and the catch retracted:



Finally. The assembled lower receivers with the catch engaged on the left and released on the right. The picture is dark but you may be able to see the part inside the receiver that trips the safety when the button is pushed:

 

I think I'm about ready to burn out if I keep it up. I'm taking a break and going to the Los Angeles area this weekend. I'll be shooting a field target match in Chino Hills with CASA. I'll be using my TF58. Maybe someday I'll use my Scotchmo Express in a match.

[lloyd-ss]

Is it just me, or do those last two pictures, when viewed as a single picture, give a bizarre effect of a hand with a big crack in the wrist just laying on table. Whew!

That case hardening compound you were using.  How does that work?  Do you need an oxy-acetylene torch?

[Scotchmo]

"Thing" is my helper.

The Cherry Red case hardening compound requires that you heat the part up until it is cherry red. I use an oxy-acetylene torch with a big tip.

[Scotchmo]

I was back in the shop today after a few days away. I did some work on the grip adapter/frame. I am still getting frustrated dealing with the backlash in that mill/drill. In these parts there is an area that I could not avoid it - I had to change direction and deal with the transition from conventional to climb milling. Mostly just cosmetic errors resulted.

I used a Harbor Freight hole saw to cut the 1-1/8" holes. Half of the teeth broke off before I finished but it got done. Not the best tool for the job. I wondered what that crunching sound was as it rotated.



I have a lot of metal to hog away.



The next picture shows the rough milled parts. I don't really have the capability to cut the small fillets and radii. I broke an 1/8" ball nose end mill while trying. I switched to a 3/16" in a couple of places.



Time to get out the files and do a lot of finish work.



I'll be starting on the upper receiver in a couple of days.

[QVTom]

Looking good   Boy, you work fast! 

I'm sure you already know this so I'm hesitant to throw it out there.  You can try to use your axis locks to add enough drag to overcome the the tendency for the cutting tool to pull the work piece to the head of the back lash when climb cutting is necessary.

Tom

[ZipSnipe]

Looking good!!

Man I can't believe you did those holes with the hole saw.  But it worked and sometimes thats what counts.
If ya got a 4 jaw chuck for your lathe you could have done it on the lathe or hunt ya a boring head for your mill. Or rough it out with an endmill and then come in with a fly cutter to clean it up.

But hey good job of making do with what ya got,, Keep it coming!!!!!

[ZipSnipe]

Ditto with what Tom said.  Climb cutting is my favorite way of milling but its not that great if you're trying to side mill lets say .250 or over , it will catch and feel like its gonna destroy the whole machine and easily ruin a part.

P.S. I see also that you're using a 4 flute endmill, while you can use it to mill aluminum it is way better to get a 2 flute cutter or just use lots of coolant with the 4 flute, it gets hotter and will melt the aluminum right onto the cutter and can ruin the cutter and the part.  I hunt down those endmill lot deals on ebay   or goto Harbor Freight

[Scotchmo]

...You can try to use your axis locks to add enough drag to overcome the the tendency for the cutting tool to pull the work piece to the head of the back lash when climb cutting is necessary.
...

I don't know if the mill/drill has an axis lock. I tried tightening the gibbs but then it hangs up at different points in the travel so I have to readjust it each time. I just leave it at the best average setting.

...
P.S. I see also that you're using a 4 flute endmill, while you can use it to mill aluminum it is way better to get a 2 flute cutter or just use lots of coolant with the 4 flute...

I figured that out when I clogged up some small four flute mills. I now use two flute for most of my aluminum cuts. I do use that large 4 flute to hog away large amounts. It seems sharper than my other mills.

[ZipSnipe]

Yeah we all learn by mistakes.  I had just recently messed up a 4 flute end mill and the part which was 1/2 aluminum pipe that I was making a slot in it, didn't take but a few seconds of milling to screw it all up.

I used to work at a mold shop with great big CNC machines that were drilling aluminum and I still being a lil green let one of the machines run out of coolant and it snapped a one inch drill bit right off with a horrible noise that went with it. And it was about a $100 drill bit and the boss was not happy.