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Go or no-go lathe question

Posted: Tue Jun 03, 2014 4:04 pm
by airsix
The good news:
I have a form 1 and plans for my 300aac suppressor

The bad news:
My lathe is a 7x14 and I can't get a bigger one until I build a workshop.


Do I attempt to single-point thread 1.5" OD GR9 titanium tube at the far-end of the bed while holding it in a steady-rest, or do I wait 2 years until I have a workshop and proper lathe?

Re: Go or no-go lathe question

Posted: Tue Jun 03, 2014 4:53 pm
by Bendersquint
airsix wrote:The good news:
I have a form 1 and plans for my 300aac suppressor

The bad news:
My lathe is a 7x14 and I can't get a bigger one until I build a workshop.


Do I attempt to single-point thread 1.5" OD GR9 titanium tube at the far-end of the bed while holding it in a steady-rest, or do I wait 2 years until I have a workshop and proper lathe?
Since this is a Form1 and you have one shot I would personally wait till you have better equipment, it can be done on the lathe you have but more risky than I would prefer personally.

You can always go with Form1 in hand to a machineshop and have them thread it for you.

Re: Go or no-go lathe question

Posted: Tue Jun 03, 2014 5:49 pm
by Dr.K
Where are you located? Someone close to you may offer their personal machine, and an chance to meet a like minded person.

Re: Go or no-go lathe question

Posted: Tue Jun 03, 2014 6:32 pm
by calinb
I'm hardly an expert machinist but I always say machine work is only 10% machine and 90% machinist. A machinist can compensate for a marginal machine with a clever setup and plenty of patience.

I've done a lot of work with 440C (annealed) and 4140 (hardened) on my hobby lathe and mill. Nevertheless, I expect my Ti projects (Forms 1s in hand) to impose a learning curve. Based on what I've read in these forums, I can't imagine that doing some threading practice on the end of a blank tube that's longer than you need for your silencer would pose a legal problem. If you botch the threads, just cut them off and try again. After you nail your threading job with confidence, thread the other end of the tube! :mrgreen:

That said, if you don't discover a thread deficiency until after you blow your end cap or tube off the end of your silencer and gun, you are screwed with a Form 1 build!

I've read that thread mills work well on titanium. Unfortunately, I don't have a CNC mill, but I plan to create a thread mill setup on my lathe. I have a milling adapter, which replaces the compound rest. It moves horizontally with the cross slide and carriage. My idea is to hold or mount a small spindle head in the adapter and drive it with a belt and pulley from a variable speed motor. It will turn the thread mill. I've been looking for the parts I need at the right price and will wait to try threading my Ti tube until after I get it working.

Finally, as evidence that you can pull-off your threading job on a hobby lathe (and at the risk of getting slightly off-on-an-interesting-topic), I submit that Doble Troble makes his own chamber reamers using only cheap Chinese hobby machine tools. He uses his home made reamers to chamber his barrels. Then he wins matches with them! Unfortunately, his howto webpages no longer exist, which described much of how he does his work. I know of only one remaining forum thread. Unfortunately, the link to the photo showing how he stuck two min-lathe beds together to make a longer bed is dead too:
http://www.sporterizing.com/index.php?showtopic=3939

If anyone is interested, I think I archived all the information documenting Doble Troble's feats somewhere and you can PM me, if you'd like to read the howto. Hopefully, I'll find the time to try to make my own chamber reamers someday!

Re: Go or no-go lathe question

Posted: Tue Jun 03, 2014 7:31 pm
by airsix
Thanks for the input, guys. I've cut/drilled/tapped a lot of 6al/4v, so I know how challenging Ti can be to machine. (For a fun time, tap a bunch of 0-80 threads in 0.100" Ti plate) That's why I'm approaching this cautiously. I definitely enjoy seeing a tough problem solved though, so I'm still considering the possible ways to pull this off with the machinery I have.

Re: Go or no-go lathe question

Posted: Wed Jun 04, 2014 12:04 am
by airsix
Follow-up:
I threw a piece of plastic pipe in the lathe tonight to see how this might work.
It's a no-go. My steady rest will only hold 1.3" stock.

Re: Go or no-go lathe question

Posted: Wed Jun 04, 2014 9:57 am
by FarmDadCO
I have one of the little 7x12 lathes . You can modify the rest " fingers " by extending the slots and get 1.5 in the rest without a problem . I don't know how the lathe would handle Ti though . The only thing i have threaded our on the end of the ways like that is Al and it worked ok for that .

Re: Go or no-go lathe question

Posted: Wed Jun 04, 2014 2:40 pm
by airsix
FarmDadCO wrote:I have one of the little 7x12 lathes . You can modify the rest " fingers " by extending the slots and get 1.5 in the rest without a problem . I don't know how the lathe would handle Ti though . The only thing i have threaded our on the end of the ways like that is Al and it worked ok for that .
This is great news! I was just thinking about the possibility of doing this but hadn't measured yet to see how much meat could come off those finger slots. I'll report back after I lengthen those slots. :D

Re: Go or no-go lathe question

Posted: Wed Jun 04, 2014 5:01 pm
by calinb
If you decide to try my single profile thread mill trick, check out the second to the last page here for speeds:
http://www.sct-usa.com/pdf/SCT_catalog_609-web.pdf

I suspect the pressure on the tube will be less than single point threading with a traditional cutter so your rest support may not need to be as robust, but I have no experience doing this yet.

For threads on our large ID tubes (large compared to the diameter of the thread mill cutting head), the AFR should be close to the NAFR. Depending on the diameters of the tube and mill, it looks like the mill spindle will need to spin about 700 to 1000 rpm and the feed speed will require turning the lathe spindle very slowly by hand (~ 1 rpm with a 4-tooth SPTM).

I'd be very interested in hearing form anyone who has tried to thread a Ti tube on a lathe this way.

Re: Go or no-go lathe question

Posted: Wed Jun 04, 2014 8:30 pm
by twodollarbill
Little Machine Shop is now offering a larger Steady Rest with a 2" opening for the mini lathes.

Re: Go or no-go lathe question

Posted: Wed Jun 04, 2014 9:20 pm
by FarmDadCO
twodollarbill wrote:Little Machine Shop is now offering a larger Steady Rest with a 2" opening for the mini lathes.
Good to know . I try not to visit their site often because it just costs too damned much by the time I check out . Lack of willpower will be the death of me , and likely the first time the wife picks up the fedex package instead of me LOL .

Re: Go or no-go lathe question

Posted: Thu Jun 05, 2014 9:25 am
by Historian
FarmDadCO wrote:
twodollarbill wrote:Little Machine Shop is now offering a larger Steady Rest with a 2" opening for the mini lathes.
Good to know . I try not to visit their site often because it just costs too damned much by the time I check out . Lack of willpower will be the death of me , and likely the first time the wife picks up the fedex package instead of me LOL .

:) :)

Welcome to TJA -"Tool Junkies Anonymous". We welcome you with open arms and
tool catalogs. Despair not. Help is all around you. We have been there and
are sympathetic to your relapses. Alas, we are all sinners here.

When the overwhelming urge invades your thoughts, overpowering desire for shinny, curvy,
whirring tools take hold, call a member ... so we can see if we should also buy it.

If God did not want men to go glazed eyed over lathes and mills he would not have
infused us with so much testosterone. And the DEA cannot stop this endorphin high drug.


We are all beyond redemption. It does not attenuate with age.

Best.

Re: Go or no-go lathe question

Posted: Wed Jun 18, 2014 1:35 pm
by airsix
Per FarmDadCO's tip, I milled out the slots in the steady rest fingers and it now easily holds 1.5" OD stock. Thanks!

Re: Go or no-go lathe question

Posted: Wed Jun 18, 2014 9:20 pm
by Scared_of_zombies
airsix wrote:Per FarmDadCO's tip, I milled out the slots in the steady rest fingers and it now easily holds 1.5" OD stock. Thanks!
What's your general location?

Re: Go or no-go lathe question

Posted: Fri Jun 20, 2014 11:17 pm
by airsix
Scared_of_zombies wrote:
airsix wrote:Per FarmDadCO's tip, I milled out the slots in the steady rest fingers and it now easily holds 1.5" OD stock. Thanks!
What's your general location?
SE Washington state