The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

Supporting all legal firearm owners, collectors, enthusiasts, shooters and competitors by promoting and encouraging legitimate gun ownership and use in the UK through unity, advocacy and discussion. To REGISTER contact admin(at)full-bore.co.uk
It is currently Tue Jun 02, 2020 4:37 pm

All times are UTC




Post new topic Reply to topic  [ 3 posts ] 
Author Message
 Post subject: Screw cutting speeds
PostPosted: Sun Mar 29, 2020 10:30 am 
Offline
Site Supporter Since 2015
User avatar

Joined: Fri Nov 05, 2010 8:27 pm
Posts: 23546
Location: The Lincolnshire Wolds, UK
Home club or Range: Hemswell Shooting Club. North Coates Butts UK. Grove Small Arms, Barton Road UK. Ulfborg Skyttecenter DK. BASC Trade Member
Screw cutting is always entertaining to my mind and something I really enjoy even though it becomes a bit tedious after a while.

For the manual machine (Chipmaster) I refer to my notes to this day, just to confirm start and finish depths, undercut at shoulder and the correct feed settings even though I know the majority of them off by heart. I use full form carbide screw cutting inserts at a zero degree in-feed angle even though the compound slide is usually set at around 25 degrees as much to add clearance to the tailstock as anything. I have a specific method of checking for squareness and still check the TPI after the first light cut to this day. Typical cuts are 0,1mm to start and half this towards the end. If it is something unusual I will use a marker pen to note a reference depth or similar on the compound slide for visual management. (The vice on the mill is sometimes covered in notes or numbers and wiped with acetone before the next job)

I also use http://theoreticalmachinist.com/Threads ... erial.aspx as my primary reference for all things Imperial albeit with the metric conversion and have also used this site to confirm some pure metric threads for some large diameter fine internal stuff (0,50mm and 0,35mm) With superb results.

I tend to screwcut at quite modest speeds on the manual when working up against a shoulder, so seldom above 350-400RPM and I always work out to in on external threads. For internal I work in to out and will very occasionally invert the tool and set it at the back. I have even run the lathe in reverse and again worked from the back however that was for one very specific job and I really should have moved it to the larger machine.

On the big machine I usually run at 650-1000 RPM with flood coolant and this video shows the machine screwcutting an 8mm x 0,75mm thread for an OAL gauge at 1000 RPM without coolant, so you get a better idea of what is happening (I cringed for the duration) I run 15.2 passes, that is 15 cuts then two spring passes which are effectively the same as the last pass and are there to overcome any deflection in the part.

You will notice the machine is CNC and in a traditional form as opposed to slant bed. It can be run as a fly by wire type manual with a 0,001mm resolution or by program derived from a CAD drawing in .DXF format. I simply draw the part, export as .DXF then import into the dedicated CAM package, specify the start points (X,Z) the feed, depth of cut and tool and generate the .PRG file which is then fired across to the Viking at the machine itself. I can change the speed and feed locally but not the depth of cut. Once the .PRG is received all that is needed is to specify the start point.

I also work to a typical tolerance of 0,01mm for most jobs which is quite tight (Many CNC shops work to 0,1mm unless specified) It is also always a cut measure cut process to start off with, I trust nothing, not even my own machines when it comes to critical jobs. Finally, you can teach an old dog new tricks, this machine arrived around the same time as my 60th birthday and the Viking and I sat down with a manual one Sunday and taught ourselves how to use it. The CAD side was not an issue, so it was mostly protocols and conventions type of stuff that we had to get our heads around.

So what speed are you screwcutting at and do you have any specific tips or tricks?


_________________
/d

Du lytter aldrig til de ord jeg siger. Du ser mig kun for det tøj jeg har paa ...

Shed Journal
Binbrook UK Live Weather


Top
 Profile Send private message  
 
 Post subject: Re: Screw cutting speeds
PostPosted: Sun Mar 29, 2020 12:37 pm 
Offline
Site Supporter 2020
User avatar

Joined: Fri Nov 12, 2010 8:27 pm
Posts: 6890
Interesting. Thanks for posting. I dont do a lot of screw cutting. With my small machine it is all manual. If I do I use carbide inserts. Most of my threads are cut with taps and dies.


Top
 Profile Send private message  
 
 Post subject: Re: Screw cutting speeds
PostPosted: Fri Apr 10, 2020 12:21 pm 
Offline
User avatar

Joined: Fri Oct 26, 2018 3:29 pm
Posts: 51
Location: Bournemouth
Home club or Range: Parkstone Gun Club
I've only ever used thread grinding machines to screwcut barrels, simply because I know how to use them well. Can happily tolerance to 0.0001"/0.0025mm but that's obviously not necessary for threading a barrel. The main limitation is length, I mount between centres and the distance between is limited so I can only do very short barrels.


Top
 Profile Send private message  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group