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View Full Version : Cutting 11.5 tpi on a Craftex B227l lathe



littleirv
01-06-2014, 02:39 PM
Hi,
Have a craftex B227L lathe and need to cut a 11.5 tpi internal thread for a pipe fitting. The lathe can cut 8, 9, 10,11, 12, 13, 14, 16... but no 11/2 threads. Does anyone know if I can achieve this through the change gears I have? I have tried to work it out myself and used a few on-line change gear calculation tools, but have come up empty. The closest i can come is 11.27 tpi- and the thread jams after 4 turns of the fitting.

Pictures of the lathe gear combinations are in another thread in this forum:
http://bbs.homeshopmachinist.net/threads/45494-Craftex-B227L-Lathe-Gearbox-noise-fix

I am working at home in my garage so do not have the luxury of hobbing my own gears.
Thx.

mars-red
01-06-2014, 04:06 PM
There are simpler methods of cutting gears than hobbing. One of the simplest methods can be seen here: http://users.picknowl.com.au/~gloaming_agnet/cq9325rev7.html

That method requires a little bit in the way of fixturing/tooling but it's all pretty simple. The accuracy you achieve is sort of proportional to the care and effort you put into making and setting up the fixture. If you took a lot of time with it I think you could make gears more than accurate enough for your need here.

John Stevenson
01-06-2014, 05:12 PM
You don't say what gears you have with the machine, also be nice to know what pitch the leadscrew is

Bob Fisher
01-06-2014, 05:37 PM
What Sir John said. I was going to say, use more Teflon tape, but that would not be a nice way to welcome a new member, especially on his very first post. Welcome to the forum. Bob.

Boucher
01-06-2014, 05:58 PM
Most pipe threads are tapered so cutting internal pipe threads is not easy even if you had the correct pitch. A pipe tap can do it but good large pipe taps are expensive. I have used an existing fitting to machine a bushing to be installed in the host part. It is easier to install a 1/2 of a short nipple and then a coupling if that would work.

boslab
01-06-2014, 06:16 PM
As you have tried it id go with welding a socket in as mr Boucher has suggested
Welcome to the forum btw, its the only intelligent conversation i get some days, talking to myself doesn't count as intelligent anymore lol
Mark

Optics Curmudgeon
01-06-2014, 06:38 PM
11.5 is a straight pipe pitch, the threads on garden hoses are an example. Oddly, this is one thing Atlas lathes are handy for, 11.5 is "native" to them.

MotorradMike
01-06-2014, 07:36 PM
Welcome littleirv.
Don't let them get you down, they are a gnarly bunch of knowledgeable folk.

The lead screw pitch is '7' guys.
We've been through this before, although quite a while ago.
Here (http://bbs.homeshopmachinist.net/threads/38980-Threading-confusion-A-bit-long). Post #11.

george4657
01-06-2014, 08:32 PM
I did an analysis of my B227L gears and came up with the following for 11.5 turns per inch:

A = 65 Tooth
B = 70
C = 105
D = 40

Formula to get this:
E = B/A = 1.077
F = C/D = 2.625
G = E/F = .410

Turns/inch = G * 28 = 11.487 turns/ inch

This formula works for all standard gears
example 10 turns/inch = 80 70 98 40 or 80 40 70 50
E = B/A = 70/80 = .875 40/80 = .5
F = C/D = 98/40 = 2.45 70/50 = 1.4
G = .875/2.45 = .35714 .5/1.4 = .35714
.35714 * 28 = 10

Not sure how the formula works but it works for all the standard listed in the manual.
I assume the factor 28 would change with different lead screws.

I found the 11.49 by trial and error. There may be a closer one but I would need a program to compute all the possible gear combinations.

Hope this helps
George

Boucher
01-06-2014, 09:15 PM
11-1/2 is the thread pitch for 1",1-1/4" & 2" NPT threads which are tapered 0.75" per Foot. There y also be straight versions of these but NPT is tapered.

littleirv
01-06-2014, 10:43 PM
The lead screw is 7tpi. (got it from here: http://www.busybeetools.com/products/LATHE-METAL-10IN.-X-18IN.-3%7B47%7D4-HP-CRAFTEX.html )
Change gears are: 30, 35, 40, 45, 50, 55, 60, 63, 65,70, 80, 98, 100, 105, 120, 125
The usual arrangement is 4 gears (A, B-C, D) - pictured at the left of the plate on the picture below.

http://gordsgarage.files.wordpress.com/2010/12/img_7255.jpg

The size of gears that I can mate up is limited-e.g., If I try a 40, 45-60, 120 arrangement, I can not mate the 40 and 45 gear-the swing arm on the intermediate shaft does not swing far enough up to mesh the gears. Same problem if the gears in the C and D positions are too large.

The closest I came-that would fit-was 8, 40-70, 63 by trial and error, mostly error. Thx for the factor of 28-I assume it is lead screw tpi * reduction b/w the head stock and the drive (A) for the gear train. I was further off than I thought.

I am looking for the proper fit as this is for a 1.5" NPT hose coupling for a 2500psi/62gpm hydraulic pump. Don't want steel filings in the hydraulic fluid, and don't want the fitting to let go when the lines are under pressure lifting round bales. (Can't use too much teflon tape or my brothers will think I'm just jury-rigging this thing together and I'll lose my street cred.)

Thx George 4657

LKeithR
01-07-2014, 01:12 AM
Cutting tapered internal pipe threads is a pain. Not only do you have to worry about the pitch but you've also got to consider the taper. If this fitting is for a tank or cylinder why not just do as suggested and buy a coupling, split it in two and weld it on. We do this all the time. You can get the fittings in STD (Sched 40), XS (Sched 80) and XXS (Sched 160) designations--one of the latter two will give you lots of wall thickness to work with. With all the oil and gas stuff happening in Saskabush now it shouldn't be hard to find what you need. Where in the flatlands are you?

littleirv
01-07-2014, 12:31 PM
Thank-you gentlemen. Next time, teflon tape.

Paul Alciatore
01-08-2014, 04:58 AM
I did run all the combinations using Excel. I filtered out only the results that were within 0.1% of the desired value.

I came up with the following four combinations that yield exactly 11.5 TPI:

A 125 // B 98 // C 105 // D 55
A 105 // B 98 // C 125 // D 55
A 125 // B 55 // C 105 // D 98
A 105 // B 55 // C 125 // D 98

They are essentially four different ways of arranging the same four gears. I am reasonably certain that they are the only combinations of the given set of gears that will come within 0.1% of 11.5 TPI.

I do not have that lathe so I have no way to determine if any of these combinations will be physically possible.

I am going to make a complete table of all such combinations of that gear set that come within the same percentage of any 1/4, 1/2, 3/4 or integral TPI value on that lathe and post it somewhere. If anybody wants me to send a copy please PM me.

C_lazy_F_Guns
01-08-2014, 06:33 AM
I tell ya maybe not what you want to hear but NPT taps are money well spent. Good ones over 1” are speedy but the $40 China ones hold up well in the bigger sizes. I fought that taper inside threading thing and it sucks. Not fun fighting taper attachment and compound inside a little hole praying you don’t run past the last pass and need to set the whole thing up again.



BTW what the heck kind of round bail contraption uses a 1-½” pressure line? I used to have a 64 ton wrecker with 2 pumps the size of 35 gallon drums and it only had 1-¼” main pressure lines on it.

Paul Alciatore
01-09-2014, 02:42 PM
I have completed the Excel threading chart and uploaded it here:

https://groups.yahoo.com/neo/groups/MachiningTips/files/Excel%20Files/Threading%20Chart%20for%20Craftex%20B2227L%20Lathe/

When using this table, if the B and C gear values are the same, a single gear of ANY tooth count should be substituted on the intermediate shaft for that pair. The actual tooth count does not matter and any gear that fits/fills the gap between A and D can be chosen. I did not have time to annotate the table to show this for all those combinations. It appears from the OEM's chart that the 80 tooth gear is generally useful for this position.

This lathe has the ability to construct compound gearing on the intermediate shaft and this creates a very large number of possible gear combinations (over 40,000). It is an extremely useful way to set up change gears. So a complete chart of all these combinations is not convenient. I have limited the entries to threads that are at 1/4" or 0.05mm intervals (10, 10.25, 10.5, 10.75, 11 etc. TPI or 1.0, 1.25, 1.5, 1.75, 2 etc. mm for examples). I had to make this choice of "useful values" to limit the number of entries. Even so, there are over 10,000 entries in the TPI table. And there are over 500 metric entries from 0.25mm to 8.5mm. Most of the 1/4 TPI and the 0.05 mm intervals are present in the table.

It lists all gear combinations for the threads that are within 0.1% of these "useful values". However, I do not have access to one of these lathes so the combinations have not been tested. Some of them may not be physically possible to set up due to mechanical limitations of the mounting provisions.

I did not have time to reduce the number of entries for each thread and without the ability to test the set ups, I may have eliminated usable ones while keeping only unusable ones. So the user is on his/her own in determining which set ups will actually work.

This table was produced using brute force methods. A working Excel sheet was created with over 16000 lines representing all possible combinations of the first three gears. Then the fourth (D) gear was changed to all possible values, one at a time, in that table and all useful combinations were copied to a separate list. A final culling of that separate list removed any lines that used the D value in any of the other positions. This was necessary because there were no duplicate gears shown in the gear list so set ups that use two, for example, 40 tooth gears would not be possible. Last of all, the separate lists were sorted by TPI or metric pitch values.

There are mathematical methods for finding a very close approximation to any gear ratio that may be desired. These methods are useful on a lathe like this for producing things like worms to match a given gear pitch. If you are interested in these techniques you can consult a text on thread cutting. Machinery's Handbook discusses this, but beware as there is some serious math content.

littleirv
01-10-2014, 10:59 AM
Thank-you Paul. You are a gentleman and a scholar.

C_Lazy: the pump is a Haldex G20-LS off of a Volvo grader--this was a warranty piece that was replaced due to noise, but my brother (heavy mechanic) took it apart and it is fine. It is a bit of overkill admittedly but can't argue with free.
I designed and am finishing off the mounting frame, loader arm and hydraulic setup for something like this: http://www.youtube.com/watch?v=43tPc0pM2jA (not the trailer).

A basic alfalfa round bale is 1600-2000 lbs depending on how wet the hay is when its baled and this machine will have to lift it 11' up at 8' out from the truck to get it on top.

Boucher
01-10-2014, 01:44 PM
I can relate to the OP's frustration on the lack of the lathe to cut the necessary thread pitch. My Nardini is missing two very common pitches. But if it had the correct pitch cutting 1-1/2" internal tapered pipe thread is difficult for most HSM types. I start by turning the correct taper 1°47'. I use the lathe to start the cut of the correct thread pitch. This helps start the pipe tap straight and true. The tailstock center is used to support the tap as it is advanced. When I run out of power/strength to turn the tap I take it to the big pipe vice and get a longer handle. I generally prefer to use a sch 40 or sch 80 steel coupling and install it. A good picture of the pump would help but... The 1-1/2" line is probably the pump suction. To add to the confusion/speculation, if it is a SAE straight thread sealed with an o-ring, it is probably metric. Teflon tape will not seal straight pipe threads.

C_lazy_F_Guns
01-10-2014, 11:09 PM
Thank-you Paul. You are a gentleman and a scholar.

C_Lazy: the pump is a Haldex G20-LS off of a Volvo grader--this was a warranty piece that was replaced due to noise, but my brother (heavy mechanic) took it apart and it is fine. It is a bit of overkill admittedly but can't argue with free.
I designed and am finishing off the mounting frame, loader arm and hydraulic setup for something like this: http://www.youtube.com/watch?v=43tPc0pM2jA (not the trailer).

A basic alfalfa round bale is 1600-2000 lbs depending on how wet the hay is when its baled and this machine will have to lift it 11' up at 8' out from the truck to get it on top.

That is one slick contraption there! That is easy livein boy! Beats the heck out of the way we used to do it. When we went to rounds I built a trailer for 10 bails but usually just took 6 so we didn’t need to tie the top. In the field we loaded with a spike on the tractor bucket then the deck tilted to just roll them off at the barn.

Then to feed the pastures we had the wonderful tumble-bug trailer that folds up/down by applying the brakes. I sure hated that thing, if a cow peed three pastures away it was too slick to make it pick up a bail! Still better than when we fed 3-wire bails though, I could bench 310 pounds in High School thinks to those 140 pound 3-wire bails so dense a hook bounced right off half of them.

C_lazy_F_Guns
01-10-2014, 11:25 PM
The 1-1/2" line is probably the pump suction.

That’s what I was thinking too, 1-½ would be about right for the supply (which is just gravity feed) from the tank. But he said it’s pressure, off a Volvo grader it could be a high flow pump.

JoeCB
01-10-2014, 11:40 PM
You just need to borrow some time on a "normal" lathe... both the South Bend and the Atlas has 11-1/2 on the QC box... along with several other strange threads, 4 -1/2, 5 -1/2, 5-3/4, 6-1/2, 7-1/2. Can't say that I have ever used them but they are there if needed.

Joe B

C_lazy_F_Guns
01-10-2014, 11:58 PM
Okay I looked up that pump here is the pump specs.
http://2.imimg.com/data2/XT/WL/MY-892394/haldex-load-sensing-gear-pump.pdf

Been a long time since I messed with these (gunsmith for years now) but if I remember right that is a swivel fitting on the pressure side. The 4 bolts hold two half flanges that retain about a ¾” pressure line poked in the big hole with an O-ring around it to seal it inside the port.

If you are making a flange fitting to bolt to those 4 holes don’t, it will never hold the pressure. Go buy the fitting to go in the hole with the two retainer blocks.

If your working on the other port with the pipe threads that is the suction side, no pressure at all there, in fact negative pressure when running. Usually that would have a hose barb threaded into it with a big hose from the supply tank just hose clamped onto the barb.

littleirv
01-11-2014, 10:15 PM
C-lazy: that's exactly what I was doing, with an o-ring on the mating face. I got the idea from local machinist who had done this type of thing with a high capacity pump off an older track-hoe> His seemed to work out. I'll have another chat with him to make sure I understood correctly.
BTW the supply line is a 2" line-and I made a flange adapter for that as well.
The pump and hydraulic spool are a closed-center system so the threaded hole in the pump casing (also about 1.5") is the pump return line to the reservoir.

C_lazy_F_Guns
01-11-2014, 11:30 PM
Maybe you can make it work but I sure couldn’t when I tried, all I made was a fancy sprinkler. No matter how I went about it the high pressure seemed to flex my plate and blow right past the O-ring. I went and paid for the correct fitting, in that configuration the harder it pushes the tighter the O-ring gets.

PStechPaul
02-17-2014, 06:42 PM
I may need to cut some 1-1/4"-11-1/2 TPI or 1-1/2"-11-1/2 TPI pipe threads for my transformer project, in copper and/or aluminum. I found that my HF 45861 lathe has a setting for 11.5, so at least it should work for this.

http://enginuitysystems.com/pix/HF_Lathe_Thread_Chart.jpg

However, I have never cut threads on the lathe so I am hesitant to try it, at least until I get some experience, and apparently such tapered threads are tricky. It's probably hardest to cut the inside threads, so I will probably get an inexpensive tap, about $35 and $50 from McMaster. But the external threads require pipe dies as well as a holder, which seem to be about $200. I'd like to learn how to cut threads on my lathe, but this may not be a good place to start, and I might not even be able to do it on my 9" x 20" machine.

http://www.mcmaster.com/#pipe-taps/=qqamb2
http://www.mcmaster.com/#standard-dies-for-pipe-threading-tools/=qqlq05 (square dies are only $47 and $64)

But I had an idea for making my own taps and dies. It seems that I should be able to cut slots in an iron pipe coupling to expose sharp edges on the inside that should be able to cut the external threads (since it will only copper or aluminum), and likewise, I should be able to mill slots into the external threads of a matching nipple or adapter, to make a tap for the inside threads. This would be something like a self-tapping machine screw.

I think I have some old iron pipe fittings of that size, and also some aluminum plate and round, so I think I might give it a try. Any ideas on whether or not this might work? I assume I will need to cut a little bit of relief into the cutting edges, probably about 7 degrees or so.

Here are some of the fittings. The plug is 1-1/4" pipe thread, about 1.67" diameter. The bushing has 1-1/2" threads, 1.92" diameter.

http://enginuitysystems.com/pix/Pipe_Fittings_1.25-1.50_0782_800p.jpg

[edit] It seems like my idea about making taps and dies may not work very well. the length of the thread and the taper are not enough to get the cut started and make the threads deep enough. The taper is 1 in 16 and the height of the thread for 1-1/4 NPT is about 0.069". So I think it needs 16 times that or about 1.1" of thread to get one thread height. The bushing has about 0.75" of thread and the range of diameter is 1.652 to 1.598, or 0.054". Actually, I think the taper is the total angle, so it would actually take 2.2" of thread to obtain the full depth of cut.

http://machiningproducts.com/html/NPT-Thread-Dimensions.html

Taper is 3/4" per foot. Angle of taper to centerline is 1 degree 47 minutes (1.78 degrees).

becksmachine
02-18-2014, 07:48 AM
However, I have never cut threads on the lathe so I am hesitant to try it, at least until I get some experience, and apparently such tapered threads are tricky.
Taper is 3/4" per foot. Angle of taper to centerline is 1 degree 47 minutes (1.78 degrees).

Yes, tricky would be an understatement!

I looked at a manual for your lathe online and I saw no mention that a taper attachment is available for it, does it have one?

See posts 5-12.

:)

Dave

http://bbs.homeshopmachinist.net/threads/62301-single-point-internal-pipe-thread-on-the-lathe?highlight=pipe+threads

oldtiffie
09-09-2014, 11:00 PM
I thought I'd come back to this quite old but not finalised thread.

The OP has a 7tpi lead-screw and wants to cut a 11.5 tpi thread.

Nobody has asked or said what the gear-drive layout really is as most or all seem to assume (for no good reason) that the lathe is a South Bend belt-driven cone-pulley and flat belt spindle drive and the first gear in the external gear train is mounted on the end of the head-stock spindle.

Not so.

The lathe is a geared head (engine?) lathe where there is a 1:4 reduction gear drive that drives an external spigot that has the first of the external gear train mounted on it.

Now put the 1:4 ratio into the external gear drive (1:7) and you will get 1/4 x 1/7 = 1/28 which is the ratio required for 11.5 tpi screw-cutting.

I have a similar lathe as do quite a few here from Canada.

So don't assume that "think so" is always the same as "know so".

Here is my lathe - the same as the OP's:

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_misc/Lathe2.jpg