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hwingo
10-23-2009, 02:19 AM
Apparently there are several buttress thread versions out and about.

1. Of the various buttress thread versions, which has the greatest axial loading strength?

2. Is there a thread (designed for axial loading) having greater strength than buttress threads? If so, what.

Harold

tattoomike68
10-23-2009, 03:19 AM
Apparently there are several buttress thread versions out and about.

1. Of the various buttress thread versions, which has the greatest axial loading strength?

2. Is there a thread (designed for axial loading) having greater strength than buttress threads? If so, what.

Harold

I made some buttress nuts for a big press break from aluminum bronze. Im sure it good for a few decades.

1 big freaking threads 6 inch kicks the crap out of 3 inch threads

2 no see #1

camdigger
10-23-2009, 11:23 AM
There's a couple of modified acme and buttress threads that have taken precedence over the plain old buttress in OCTG, but one of the primary considerations on those threads is sealing, not just axial loading.

Presumably, you're using this for a joint under tension or moving a device? Or are you joining pipe?

HSS
10-23-2009, 01:45 PM
my machining book says square threads are the strongest but are difficult to machine. (just reading that this morning in the thrown room) :D

Patrick

camdigger
10-23-2009, 02:00 PM
Wikkipedia notes that the buttress thread for is asymetric. Has virtually equivalent strength of square in one direction, but less in the other. http://en.wikipedia.org/wiki/Buttress_thread

Wikkipedia also claims square thread is not as strong as a trapezoidal form http://en.wikipedia.org/wiki/Square_thread_form like Acme http://en.wikipedia.org/wiki/Acme_thread_form, but with different shoulder angles... http://www.roymech.co.uk/Useful_Tables/Screws/Trapezoidal.html

At least, that's what Google tells me...

hwingo
10-23-2009, 02:10 PM
Presumably, you're using this for a joint under tension or moving a device? Or are you joining pipe?

I am using this for a joint under tension as well as moving.

Thanks guys for your replies.

Harold

agrip
10-23-2009, 02:52 PM
In the case of high (make that HIGH) axial loads, the buttress does NOT deflect much. At first blush this can appear as a huge advantage.

The problem is strain gage testing demonstrates large stress concentration at the root of the thread and the second third and fourth threads do not get the typical shared load.

Therefore Acme or Trapezoidal with filleted roots, are strong, load sharing, easier to machine, especially with a muti-point tool, and much less likely to suffer a sudden fatigue failure.

Hth Ag

Black_Moons
10-23-2009, 03:14 PM
So buttress threads are really just cool looking and not good for much else? :P

hwingo
10-23-2009, 03:20 PM
The problem is strain gage testing demonstrates large stress concentration at the root of the thread and the second third and fourth threads do not get the typical shared load. Hth Ag

Some firearm locking lugs "appear" to be fabricated using buttress threads. I do believe the breach on some cannons use a buttress thread. My thoughts were on the order of fabricating a bolt and receiver locking lug using butress threads (of course using correct metal). Hearing that the first thread take the major load causes concern.

Harold

juergenwt
10-23-2009, 04:28 PM
It seem to me that a buttress thread as per DIN 2781 used for hydraulic presses would be a top contender. The thread is 45 deg..
Look here about half way down under "S" DIN 2781: http://mdmetric.com/fastindx/t44u.pdf
Or here: http://mdmetric.com/tech/stds/din202de.htm

Black_Moons
10-23-2009, 04:52 PM
And the size for 'hydrolic press' buttress threads is 100~1100mm according to that page. I bet at that size any thread would do.

Can anyone point to an actual tested reason to use buttress threads besides 'they look cool'? and 'look like they should be stronger'?

Maybe im just 'thread jaded' after my $600 kurt vise came with what looks to be a standard V threadform (On a 1" or thicker shaft mind you) insted of the allmighty acme that most cheap metalworking vises have (On a 1/2"~3/4" shaft usally mind you..)

lazlo
10-23-2009, 04:53 PM
my machining book says square threads are the strongest but are difficult to machine. (just reading that this morning in the thrown room) :D

I would think that acme threads are stronger given the same OD and pitch, since they don't have the stress risers at the interface with the shaft diameter?

More importantly, buttress threads are designed to be much stronger in one direction than the other (the direction opposite the saw tooth), which is why they're usually seen on vises, presses and such...

camdigger
10-23-2009, 05:10 PM
Another factor that gets ignored when assessing threads is that a thread with an angled shoulder will exert a force radially outward when put under load, not just axially.

It is not uncommon for this outward force to plastically deform couplings on OCTG if they're over torqued when made up or in use. This is most apparent in OCTG as the connections are often tapered as well....

dalee100
10-23-2009, 05:18 PM
Hi,

I've made ball screws for fly wheel presses up to 100 ton with buttress threads. They are somewhat of a pain to single point as the chip load gets kind of high on the tool. Particularly with 4 pitch threads.

I did see an old 4" machinist's clamp that had buttress threads on the screws. The old guy had made it years ago when he was an apprentice. Glass smooth and no play at all even after 30 years of use.

I don't recall too well, but didn't Sako or Tikka use buttress threads once for locking the breach of a rifle model?

dale

gwilson
10-23-2009, 05:50 PM
Buttress threads were used on cannon,as suggested earlier. The 16" guns on battleships,and cannon in other applications use buttress threads. Their breeches get very tricky,with the buttress threads cut on several different diameters in the same breech.

hwingo
10-24-2009, 02:33 AM
Well, I'm going to give this a go using a 4 TPI American Buttress for total length of 1.25 inches. We'll see what happens.

Harold

oldtiffie
10-24-2009, 03:49 AM
Harold.

I would suggest that you consider "tilting" the tool by the helix angle of the thread:
http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting16.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting17.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting18.jpg

If it were me, I'd cut the thread in three stages:
- cut the centre as for a "square" thread;
- cut the 45 deg ("trailing") side; and then
- the 90 or 75 or what-ever angle the lead side of the thread is.

Apply the required three different "side" and "back" rakes for each stage/phase.

If I recall correctly, cannons were muzzle-loaded where-as larger rifled naval guns and army artillery pieces had swinging breeches blocks that were engaged with "interrupted" acme threads - is "swing", "insert", and rotate the breech block to engage the interrupted thread/s in the breech-ring.

Smaller/later guns had sliding (usually vertical but sometimes horizontal) breech-blocks that slid in guide-ways in the breech ring.

hwingo
10-24-2009, 05:27 AM
Tiffie,

That's some interesting material you've provided. I've briefly scanned the material you've submitted. It's quite late here and I will read in earnest, for content, tomorrow morning.

I have ordered the Carmex internal and external tool holder with complimenting internal and external indexable carbide inserts for cutting 4 TPI American buttress. In passing, I considered 3 TPI but settled on 4 TPI. The design will be interrupted threads ultimately culminating in a tri-lobe design similar to the 50 cal BMG bolt action rifle that I made (of which you have pictures).

Cutting 40 degree cams in the 50 cal receiver's tri-lobe locking lugs proved to be a pain in the rear. As you may recall, each locking lugs on the bolt had one inch of thickness for support behind the locking interface complemented with one inch of thickness behind each lug on the receiver having a total of two inches of support with each lug. This design has worked nicely .... BUT .... camming on closure or on opening is not *instant*. Either on opening or closing, the bolt/bolt handle must travel a very slight distance before camming truly begins making case extraction of a fired case *slightly* snug until full camming begins. An inordinate amount of time was spent fabricating the bolt's locking lugs as well as the receiver's locking lugs.

I am hoping to decrease bolt and receiver fabrication time by instituting the buttress thread locking design. I am rather confident that 1 1/4" of interrupted thread on the bolt and another 1 1/4" of threads in the receiver will accommodate safety. No less, I am thinking that camming will begin immediately on extraction because of helical engagement of thread interface. As soon as I begin lifting the bolt handle, *smooth* positive .... near effortless extraction will begin as a result of lock-up on helical threads. Four TPI should provide an exceptional "throw" as compared to my current design.

The cartridge will be patterned off the 50 BMG case (as before), however, while keeping case length the same as an original 50 BMG, I will blow out the shoulder to 32 degrees and neck down the case to .416 cal. The projectile should fly somewhere between 3500 - 3700 feet per second making this an exceptionally long distance, flat shooting target rifle.

Regarding buttress threads on some cannons, though I was not succinct when mentioning cannon threads, I really meant to imply that interrupted buttress threads were used on breach loaders. Sorry for the confusion.

Harold

oldtiffie
10-24-2009, 07:07 AM
Harold.

A couple of clarifying points if I may.

I was a Chief Ordnance Artificer long ago (hence my tag) in the OZ Navy and naval armament was my forte' and my interest. Needless to say a bit of the history was pretty well inevitable.

The gun interrupted buttress (some were acme too) had beveled or "rounded" "leads-in" as on the gears in many gear-boxes to facilitate engagement. Obturation was a problem as many had (silk) bags of cordite or gun-powder (could be varied - as in howitzers etc. - for range or changes of elevation for similar ranges - ie "flat" trajectory as for a naval gun - for longer range and vertical ship side targets - or "high" as in a mortar for targets on the ground - for "lobbing" - also used for Naval Gunfire Support against shore-based targets - including firing at targets on the other side of a hill etc.). "Mortar" was used for "illumination" (aka "Star shell") for firing past a target (ship) to illuminate the target in silhouette. Obturation was not a problem when the charge (cordite or gun-powder) was in (naval) brass cartridge cases - as in a rifle or machine gun - which expanded into the chamber - but the "head clearance" was important so that the case did not burst in the barrel and that extraction was as easy as possible on the extractors. A "cooker" or a "hang-up" are experiences that can be done without. There's enough to be concerned about with all the people yelling (to be heard) and not too mention all that high-pressure high temperature hydraulics and HP air and screaming machinery - as well as all the shell and cartridge in the gun turret which in turn was right over the shell room and magazine - which were right next to some of the fuel tanks.

It was much nicer on a rifle/pistol/machine-gun range.

Witnessing the "proof firings" or new or re-manufactured naval ordnance was something to see as until then the ordnance had not been "fired" or "proved".

Now, back to the buttress thread.

I always "tilt" my screwing tools unless there is a large "chip-breaker" (as on the front of a parting tool) so as to ensure a positive side rake on the "trailing" flank.

I don't like "flat-topped" screwing tools.

As regards the "tilt" for the helix angle.

If you were plunging "straight in" for a form tool or a parting tool on a "ring" or "groove" the tool would be horizontal and the groove vertical (it has a zero helix angle) - ie they would be at right angles to each other and all is right with the world. I'd guess that none of us would either contemplate not actually "tilt" the tool left (most cases - for right hand threads) or right.

If the tool is to "follow" the line of the groove (thread) it must be tilted to suit the helix angle else the trailing edge will have a negative side rake and will "rub" instead of "cut". The leading edge will or may have an excessive side rake (which may tend to make the tool "dig in") as well as a reduced side clearance which will or may make the tool "rub".

Here are some tools that I have that may assist:
http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_misc/I-Fanger2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_misc/I-Fanger3.jpg

The parting tool ans screwing tools are easily adjusted for height and the screwing tool can be tilted left-right to suit the thread helix. Both are simply sharpened on the pedestal grinder (by hand) using the plastic template.

Other than that I use a bit of round HSS in a boring bar (same size) holder for external threads and use a boring bar with a round HSS tool in it. Both are tilted for the helix angle.

"Tilting" is usually not required for thread with a helix angle not more than 5 degrees (which covers most common threads).

If I were doing that buttress thread of yours. I'd use a common parting tool (type of) cutter to plunge in a the zero degree mark (for the "guts") - just a bit less wide than the finished width of the flat at the bottom of the thread.

This next bit should be familiar!!!

Using same parting tool (in a "tilting" holder or made "tilting" - to suit the helix angle) set the top-slide (aka compound slide) to 45 degree left (or as required), lock/clamp the cross-slide, and just plunge straight in with the top slide. Then 5 degrees right (or to suit), clamp the cross-slide and use the top-slide and plunge right in.

If you have your tool honed razor-sharp with straight edges and with the correct "tilt" and side clearance and side rake angles with the lathe on slow speed and using lots of good cutting-tapping oil (on a brush will be fine) start "shaving off" on the left and right flanks (one at a time) and you should be good to go.

So much for the "external" (male) thread.

The internal (female) thread uses the same principles but different settings. If the internal thread is at or near a "dead end" (blind hole/bottom) I'd suggest running the lathe in reverse and starting at the bottom of the hole and "work out" - toward the tail-stock. Its safer and less "wearing/stressful".

I hope this helps.

If you have any other queries or questions - or suggestions - please either post them here or else past me by PM or email.

hwingo
10-24-2009, 10:05 AM
Harold.

I always "tilt" my screwing tools unless there is a large "chip-breaker" (as on the front of a parting tool) so as to ensure a positive side rake on the "trailing" flank.

I don't like "flat-topped" screwing tools.

As regards the "tilt" for the helix angle.

If you were plunging "straight in" for a form tool or a parting tool on a "ring" or "groove" the tool would be horizontal and the groove vertical (it has a zero helix angle) - ie they would be at right angles to each other and all is right with the world. I'd guess that none of us would either contemplate not actually "tilt" the tool left (most cases - for right hand threads) or right.

If the tool is to "follow" the line of the groove (thread) it must be tilted to suit the helix angle else the trailing edge will have a negative side rake and will "rub" instead of "cut". The leading edge will or may have an excessive side rake (which may tend to make the tool "dig in") as well as a reduced side clearance which will or may make the tool "rub".


The parting tool ans screwing tools are easily adjusted for height and the screwing tool can be tilted left-right to suit the thread helix. Both are simply sharpened on the pedestal grinder (by hand) using the plastic template.

Other than that I use a bit of round HSS in a boring bar (same size) holder for external threads and use a boring bar with a round HSS tool in it. Both are tilted for the helix angle.

"Tilting" is usually not required for thread with a helix angle not more than 5 degrees (which covers most common threads).

If I were doing that buttress thread of yours. I'd use a common parting tool (type of) cutter to plunge in a the zero degree mark (for the "guts") - just a bit less wide than the finished width of the flat at the bottom of the thread.

This next bit should be familiar!!!

Using same parting tool (in a "tilting" holder or made "tilting" - to suit the helix angle) set the top-slide (aka compound slide) to 45 degree left (or as required), lock/clamp the cross-slide, and just plunge straight in with the top slide. Then 5 degrees right (or to suit), clamp the cross-slide and use the top-slide and plunge right in.

If you have your tool honed razor-sharp with straight edges and with the correct "tilt" and side clearance and side rake angles with the lathe on slow speed and using lots of good cutting-tapping oil (on a brush will be fine) start "shaving off" on the left and right flanks (one at a time) and you should be good to go.

So much for the "external" (male) thread.

The internal (female) thread uses the same principles but different settings. If the internal thread is at or near a "dead end" (blind hole/bottom) I'd suggest running the lathe in reverse and starting at the bottom of the hole and "work out" - toward the tail-stock. Its safer and less "wearing/stressful".

I hope this helps.

If you have any other queries or questions - or suggestions - please either post them here or else past me by PM or email.

Good Morning Tiffie,

It's about 0430 and I can't sleep any longer. Seems the older I get the less I sleep and the more tired I get.:(

Now, on to cutting a buttress thread. I've never done one before. For that matter, I had never cut a standard 4 TPI until last weekend and it seemed to take forever.:eek:

I mentioned that I had purchased the carbide inserts that were specifically designed to cut the American Buttress Thread. The inserts I specifically ordered are "pre-shaped" so as to cut a "proper formed buttress thread" (assuming I don't screw up) meaning that, along with other things such as angles etc., the crest and valley will be rounded to reduce the possibility of shear points. I *assumed* much when selecting these inserts, e.g., I am assuming the cutter will be slowly plunged (using multiple passes) until the thread is formed rather than using the compound that's been turned to 29.5 degrees as with a standard thread. Stated differently, I have assumed that the cross feed is advanced with each successive pass rather than a turned compound.

Have I assumed too much?

Am I hearing you say that it might be easier to first "remove a great deal of metal" before attempting to bring the thread to form? Is that the reason you have discussed using a parting tool?

Harold

Carld
10-24-2009, 11:09 AM
I have only cut a couple of buttress threads and one of them was for an Excelo power hack saw. It used a half nut to lay the buttress thread screw in and tighten the jaws. The problem was the straight side was angled so it caused the screw to finally jump out of the half nut after some wear. I undercut the thread on the screw and half nut so it pulled the thread screw into the half nut rather than push it out. It worked great after that.

The one time that I cut a complete thread rather than a repair/recut I did see a heavy chip load as the thread neared completion. When I cut square threads I set the compound at 90 deg to the crossfeed because I only cut one side of the thread at a time. It may be the wrong way but it's the only way I could do it without breaking cutters. You may have to do the same with the buttress thread.

There seems to be many forms of the buttress thread but I had not seen them used in cannons but then, I haven't seen that many cannons.

Tiffle, how did you go about cutting a buttress thread? Did you cut both sides of the thread at the same time or one side at a time and make finish clean up passes to chase both sides at the same time?

oldtiffie
10-24-2009, 11:22 AM
Hi Harold.

You've got it pretty right with the use of the "shaped" carbide tip.

Can you post some pics of it so that I can see the "shape" from the front and back of it please?

You can "plunge in" to remove the bulk of material to be removed by having the top-slide in its normal "90" or "0" (depending on your lathe settings) position (parallel to the lathe axis and 90 degrees to the cross-slide).

Plunge in and after each cut move the tool left and/or right to eliminate or reduce the cutting load by mainly cutting on one flank (the leader) by "slacking-off" on the other "trailing flank". Providing you keep within the finished thread profile/shape/envelope you will be OK. Just move left/right no more than half of the depth of cut and you will be OK.

I don't know how slow your lathe will go, but the material/job may need a "dead slow". I've often used two chuck keys in the chuck - one in each hand - and "walked" the chuck and job around. A hand-operated lever in the end of the lathe spindle (with the quick-change/"threading/feeding" gear-box aka QCGB remaining engaged and the spindle drive gears in "neutral") will help no end.

As in all these things, I'd advise caution and "hastening slowly" until you have the procedure well in hand - on some scrap/test pieces.

"Hogging" and "tear-ar$ing" are not the orders of the day here.

"Slowly, slowly, catchee monkey".

hwingo
10-24-2009, 01:31 PM
Hi Tiffie,

I'll be more than happy to provide images of the inserts. I expect them to arrive today. If they don't arrive today then I suspect they will arrive on Monday. Regardless, as soon as they arrive I will provide images per your request.

In passing, Carld posed a question in his latest post which you may have missed. Maybe you could elaborate a wee bit with regard to his question.

Harold

Black_Moons
10-24-2009, 04:29 PM
Im not exactly sure if hand turning with carbide inserts is a good idea.. seems any time iv ever stoped turning and forgot to retract the tool before the lathe stops with a carbide insert, it snaps badly.. mind you thats usally with 0.01+ passes.

juergenwt
10-24-2009, 04:56 PM
Black Moons - hwingo did not say anything about the size of the thread.
All he asked for was an answer to what buttress thread would be the strongest.

hwingo
10-24-2009, 05:44 PM
That's correct. I did not refer to hand turning with carbide, however, I fully agree with Black Moons regarding breakage. I too have experienced breakage time and again when attempting to retract a carbide cutter from work that has stopped.

Going back to the original subject, I believe the general consensus is, a buttress thread is quite strong and may serve my purpose. We will soon see if 4 TPI works.

Harold

gwilson
10-24-2009, 05:50 PM
Never stop a carbide tool in a cut. It will always break.

oldtiffie
10-24-2009, 06:53 PM
Hi Tiffie,

I'll be more than happy to provide images of the inserts. I expect them to arrive today. If they don't arrive today then I suspect they will arrive on Monday. Regardless, as soon as they arrive I will provide images per your request.

In passing, Carld posed a question in his latest post which you may have missed. Maybe you could elaborate a wee bit with regard to his question.

Harold

Sorry Harold.

Here is Carld's' post (my emphasis):


I have only cut a couple of buttress threads and one of them was for an Excelo power hack saw. It used a half nut to lay the buttress thread screw in and tighten the jaws. The problem was the straight side was angled so it caused the screw to finally jump out of the half nut after some wear. I undercut the thread on the screw and half nut so it pulled the thread screw into the half nut rather than push it out. It worked great after that.

The one time that I cut a complete thread rather than a repair/recut I did see a heavy chip load as the thread neared completion. When I cut square threads I set the compound at 90 deg to the crossfeed because I only cut one side of the thread at a time. It may be the wrong way but it's the only way I could do it without breaking cutters. You may have to do the same with the buttress thread.

There seems to be many forms of the buttress thread but I had not seen them used in cannons but then, I haven't seen that many cannons.

Tiffle, how did you go about cutting a buttress thread? Did you cut both sides of the thread at the same time or one side at a time and make finish clean up passes to chase both sides at the same time?

Answer:
take the bulk out with a "parting" tool (tilted) by "plunging" for the centre and then use the same tool to rough out the sides by using the top-slide set at the side angles of the buttress - ie 0 or 5 degrees on one side and 45 degrees on the other. Use "tilted" "left" and "right" facing tools to clean up and finish the side face - plunge cut - small "bites". Do one face at a time. It works really well with a good HSS tool where "stopping" is less of a problem or not a problem at all.

There are many grades of TC inserts but I'd guess they'd be a lot more limited than normal for screwing inserts. The TC insert needs to be diamond-honed to a very fine edge as anything lass will require the tool edge to "push up" a "lump" to "get under" to "get started". A good tool - TC or HSS - with a good edge will cut a very fine swarf.

If I had a choice with "hard to turn/screw" stuff, I'd use a "Stellite" tool - as hard and as tough as buggery (that's a lot!!) - but its hard to come by and is even harder to grind and hone but its marvelous for shock/impact/start-stop loads/cuts.
http://en.wikipedia.org/wiki/Stellite

http://www.google.com.au/search?hl=en&source=hp&q=stellite+6&meta=&aq=0&oq=stellite

"Walking" the chuck (two chuck keys) is similar to "barring over" the fly-wheel on a large diesel engine or compressor - and can be made to be "non-stop" - with practice.

Carld
10-24-2009, 09:01 PM
Tiffle, that's the same way I did it except for using a parting tool to rough it out. I also use Cobalt HSS for threading a lot. It's tough, don't chip and holds an edge well.

oldtiffie
10-24-2009, 09:24 PM
Thanks Carld.

Doing it this way makes it more possible to do big threads on smaller lathes.

Needing "big/stiff/solid" lathes for what is a relatively simple task done to disadvantage is an exercise in futility (and stupidity) due to poor use of tools and appreciation and application of relativley simple mechanics/vectors in the "one true/traditional" way. If nothing else I guess it justifies needless expense on bigger but not necessarily better "heavy" machines - or "good old American Iron" as the main sub-plot.

I would not have thought that "hogging and flogging" - "tear-ar$ing" too - was a necessity in a home shop - or too many commercial shops either. Driving/running a machine hard within its capacity is not "flogging".

Some might like to recall or know that a lot of "big" - and multi-start - threads were cut on small South Bend lathes and the like in the early part of Apprenticeships in Trade School shops to show what really can be done on a small machine. It was also a task to find out why it could be done by some and not others - people and machines.

Carld
10-24-2009, 09:37 PM
Yep, I'll never forget the first time I tried to cut a square thread on both sides of the thread. Even with good side clearance relief it went good for a few passes and then it grabbed. Once I got calmed down again I reground a tool narrower than the finish thread and cut one side at a time with the compound set 90 deg from the cross slide so I could move it back and forth to get the right form and chase the right side of the thread.

Black_Moons
10-25-2009, 04:26 PM
So stoping turning with HSS still in the work is usally fine for the tooling?

andy_b
10-27-2009, 06:52 PM
it looks like what has been posted mainly deals with cutting the buttress thread screw. how do you cut internal buttress threads for the nut? or more appropriately, how do you even know if you are cutting the correct thread form since you really can't see the insides of the nut as well as the exterior of a screw?

i ask because i need to cut a new nut for an old vise, and it is a buttress thread.

andy b.

ps-i didn't really know what a buttress thread was until this thread was started. when i pulled the vise apart today i thought, "hey, that is a buttress thread!" :)

beanbag
10-27-2009, 07:23 PM
(never mind)

hwingo
10-28-2009, 01:25 AM
Hi Andy, et. al.,

My inserts and tool holders arrived today. As promised, I have taken pictures of the insert (front and back). My film is currently drying and as soon as drying is complete I will scan the film and provide images of the insert (~1 hour from now).

Andy, I have never cut a buttress thread but I'm about to (internal and external). I will be using Carmex tool holders (with anvils) and Carmex carbide inserts good for up to (or down to depending on the way one thinks) 3 TPI. My intention is to cut 4 TPI. I do not have a thread pitch gauge for buttress threads. I don't even know where to get one. I will cut the external thread until the major diameter is "pointed up" then cut the internal thread to "fit" the external thread. I may be doing this all wrong BUT I will cut the internal thread until the external piece barely begins to thread into the internal piece. At that point I plan to use Never-Seize mixed with lapping compound and prepare myself for a long night of lapping the two pieces until a positive, tight fit is achieved.

Andy, the internal cutter is shaped opposite the external cutter; that way the two threads compliment each other when the job is complete. To the best of my knowledge there are several different buttress designs. Some may have a "vertical angle" of five degrees where others may have an angle of 7 degrees or even 10 degrees. The other side of the thread is usually 45 degrees but I can only assume that this too can or is altered to a design that best fits the application. I have chosen the 5 degree angle cutters with the other side being 45 degrees. With limited equipment in my shop, I have no way to precision grind buttress thread cutters much less complementing cutters therefore I bought a compliment pair obviating the need to attempt grinding a matching pair.

I really don't know how my thread took on a flare for addressing carbide breakage when the work piece stops as the carbide tool is actively engaging the work but lets say two things about that subject:

1. This is not the subject of this thread thus the thread has gotten off course.
2. I never ..... ever ..... intentionally leave my cutter touching the work piece if power to the lathe is to be turned off. There have been times that I have tripped a circuit breaker or a power outage has occurred ..... which is no fault of my own all the while being totally unexpected ..... resulting in my carbide cutter breaking all to hell. So this is not my standard of care thus such is not practiced. Hopefully this will help to eliminate the need for any further discussion regarding carbide breakage and help get the topic back on track.

Pictures to follow soon.

Harold

hwingo
10-28-2009, 03:01 AM
Tiffie,

Here are the top and bottom images of the external buttress thread insert. I did not shoot images of the internal threading insert since it has the same appearance but opposite. Scale is in inches.

Harold

http://i234.photobucket.com/albums/ee38/hwingo_2007/ButtressThread1.jpg

http://i234.photobucket.com/albums/ee38/hwingo_2007/ButtressThread2.jpg

andy_b
10-28-2009, 10:46 AM
Harold,

what is the internal diameter of the piece you will be doing the internal threading on? the threaded rod on the vise i need to fix is about 3/4" OD, so i will need a toolholder and insert that look like they will be smaller than what you bought. if i'm going to purchase something similar to what you did, i want to make sure i get the correct size. could you post a photo of the entire setup you will use to cut the internal threads (the insert holder, the insert, and the tooling holder you are using)?

thanks,

andy b.

hwingo
10-28-2009, 02:55 PM
Harold,

what is the internal diameter of the piece you will be doing the internal threading on? the threaded rod on the vise i need to fix is about 3/4" OD, so i will need a toolholder and insert that look like they will be smaller than what you bought. if i'm going to purchase something similar to what you did, i want to make sure i get the correct size. could you post a photo of the entire setup you will use to cut the internal threads (the insert holder, the insert, and the tooling holder you are using)?

thanks,

andy b.

Andy:

I have yet to determine sizes other than knowing the size and type of thread that will be used. I will first do everything in aluminum so I can determine size and work out "bug" I may encounter.

The tool holders I received are MASSIVE! Before doing anything toward cutting threads I will need to alter the size of my tool holders so they will fit my lathe. Once this is done I will be able to tell you more. When I cut a standard 4 TPI, I think the depth of the thread was around .190". I am assuming that a similar depth will result when cutting the buttress thread. When I have completed alterations I will post some images.

Harold

andy_b
10-28-2009, 05:07 PM
Harold,

THANKS!!!!! i look forward to it.

andy b.

hwingo
11-01-2009, 04:58 PM
Andy,

I modified my external buttress thread insert holder and cut these threads yesterday morning. This is 4 TPI. The OD is 1.125 and the tool was advanced to a depth of 0.17401". Later I will take pictures of the modifications.

Harold


http://i234.photobucket.com/albums/ee38/hwingo_2007/ButtressThread3.jpg

Boucher
11-01-2009, 06:46 PM
Harold, This link to Tool Flo in Houston minght be of intrest to you.

http://www.toolflo.com/cats/On%20Edge.pdf

Their background is related to the oil industry and the large and strange threads. Their basic orientation of on edge threading might not work in the smaller diameters for a rifle bolt but they make some quality threading inserts/tooling.

andy_b
11-02-2009, 12:16 AM
Harold,

that came out great! certainly looks like a buttress thread to me. when will you build up the courage to try some internal ones? :)

andy b.

hwingo
11-02-2009, 12:55 AM
Harold,

that came out great! certainly looks like a buttress thread to me. when will you build up the courage to try some internal ones? :)

andy b.

Hi Andy,

I will cut internal threads as soon as I fabricate the tool holder for my insert. As previously stated, the Carmix internal holder is much too large. I will have to fabricate the tool holder from 1/2" 4140 ground stock. Once that's fabricate then I will cut the internal threads. Most likely I will do that near the end of the week.

Harold

hwingo
11-02-2009, 12:57 AM
Harold, This link to Tool Flo in Houston minght be of intrest to you.

http://www.toolflo.com/cats/On%20Edge.pdf

Their background is related to the oil industry and the large and strange threads. Their basic orientation of on edge threading might not work in the smaller diameters for a rifle bolt but they make some quality threading inserts/tooling.

Byron,

Thanks for that information. I will tuck that away for future use.

Much appreciated,

Harold

andy_b
11-10-2009, 09:19 PM
Harold,

Just wondering if you tried any internal threads yet. I won't get to my project until some time in the winter, so I have no urgent need for the info.

andy b.

hwingo
11-11-2009, 02:07 PM
Harold,

Just wondering if you tried any internal threads yet. I won't get to my project until some time in the winter, so I have no urgent need for the info.

andy b.

Hi Andy,

I have yet to make internal threads. I am trying to reach a semi-stopping point on an ongoing project. As previously mentioned, the external holder was modified and used with success but the internal holder (which came as a compliment to the internal insert) is too large to fit in the 0.785" dia hole so I will need to make a holder that will accommodate the insert as well as the hole size.:rolleyes: Having to do this gripes my butt however it's necessary.

Hopefully I can get the internal holder completed in the next several weeks. As soon as it's complete and threads cut, I will send a post with image.

Harold:)

andy_b
11-11-2009, 07:17 PM
THANKS!!! Sounds great! My timeline for my project is sometime in 2010 or 2011. :)

andy b.

hwingo
12-27-2009, 01:14 PM
Hi Andy,

I had time over Christmas to make the buttress thread insert holder and to also do some internal threading.

My hole is .930" dia so my "homemade insert holder" just barely fit inside the hole. My threads are 4 TPI and they were cut to a depth of .162". The male piece (cut previously) was 1.250" dia and threads were cut to a depth of .160". The two fit quite nicely.

Enclosed are two images of my threading tool and the finished female piece.

Harold


http://i234.photobucket.com/albums/ee38/hwingo_2007/ButtressThreadcopy2.jpg


http://i234.photobucket.com/albums/ee38/hwingo_2007/ButtressThreadcopy.jpg

Carld
12-27-2009, 02:23 PM
Very nice job Harold and I like the threading bar you made too.

hwingo
12-27-2009, 11:21 PM
Very nice job Harold and I like the threading bar you made too.

Hi Carld,

Thanks for the message. Like all things newly attempted, most are not without some issues. I had slight issues with this first attempt at internal buttress threading. With that being said, on close inspection I definitely experienced "chatter". My tool holder is only .750" dia and though I took only .002" depth cut with each pass, as my threads got deeper visible chatter was detected. I can only assume that had I used a very rigid bar such as the one designed for use with the Carmex 4 TPI buttress thread, chatter would have been practically undetectable on visual inspection.

Toward the end, I made several passes without advancing my cutter with hopes I could rid the surface of visable chatter but for the most part it was to no avail. Maybe chatter will be less in 17-4 SS or 4140 (my choice of metals for what I fabricate).

Harold:)

Carld
12-28-2009, 12:41 AM
Tell you what you can try. Take the bar in your hand and with the lathe running at the slowest speed run the bar in to chase the thread. If it hangs at all let go of the bar and hit the foot brake if you have one.

I have done this to chase an internal thread and it does work on V threads or Acme but don't try it on a square thread and that is from the horses mouth that did try it.

andy_b
12-28-2009, 02:09 AM
Harold,

That came out excellent! Thank you for following up!!!!
So, any tips or drawings on the internal holder? The internal cutter is not the same as the external one, correct?

andy b.

hwingo
12-28-2009, 03:58 AM
Andy,

Why would you use the quote at the bottom of your reply from Tattoomike68 when responding to my post? The quote he made was directly pointed at me and was intended to offend me. Turns out that my idea was not "dumb as hell". Have I offended you in some way?

Harold

Machinist-Guide
12-28-2009, 04:54 AM
Buttress threads are used in mechanical stamping presses. They are designed to handle the constant pounding of a high speed press. The face of the thread is a 90deg. that serves as the surface for pushing. The back of the thread is a 45 deg. that serves as a gusset to support the face of the thread.
As for load moving they are good for pushing but not very good for pulling.

oldtiffie
12-28-2009, 10:12 AM
Harold.

Try this for starters:
http://www.google.com.au/search?hl=en&q=strength+of+buttress+threads&btnG=Search&meta=&aq=f&oq=