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December 28, 2013 at 1:47 pm #54349
Beautiful work William!
Congratulations!
BobDecember 28, 2013 at 6:29 pm #54350William:
Is this what you’re talking about?
http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=950317&PMAKA=235-7050
It’s on my wish list too!
Later,
TomDecember 28, 2013 at 10:27 pm #54351hey Tom, possibly something like this. http://www.ebay.com/itm/NEW-ATLAS-CRAFTSMAN-9-12-LATHE-ER-32-COLLET-CHUCK-10-COLLETS-WRENCH-USA-MADE-NEW-/161180488640?pt=BI_Tool_Work_Holding&hash=item25871b13c0 but I am not sure yet. William
December 29, 2013 at 6:32 am #54352William:
After actually reading throught this thread, I see that you are using this on a Craftsman Atlas lathe.
You really are advancing in your efforts. You deserve congratulations for both your efforts and your posting this in such detail! Superb my friend!!!
One thing that Tublcan has is a complete in depth course for the Craftman/Altas lathe. One can get it in three modules – Beginning/Intermediate/Advanced, or you can buy the entire thing. I’ve been thinking about taking it and I don’t even own one of those lathes.
Tublecain’s new name is “mrpete” so don’t be confused by that. Heck, you probably don’t even need this by now, but I thought I’d post it for any poeple like me here who need all the help they can get.
In the Keith Fenner YouTube videos I saw that at one time you could get a 20% discount on MRPETE’s course by using the keyword “GETERDONE”. (His company phrase)
Any, there it is!
Later,
TomDecember 29, 2013 at 10:01 am #54353Hey Guys, thank you for the wonderful words and encouragement, I did come up with a workable screw BUT, in reference to David asking to post how I did it, I have to confess[/i], It was “by gosh and by golly”. I had bits and pieces of information, I made 4 or 5 attempts,(possibly more as I most likely tried to forget one or two) The threads are not perfect and the way I cut them on the lathe was likely wrong. I have since read and investigated more about the thread cutting process and will be putting that information to practice. In the end I know it will be a much easier and accurate process. When I learn this way I seem to be able to retain and increase the knowledge needed much faster as it makes more sense to me on how and why, trial and error so to speak. Being careful so as not to damage the machine or myself, I like to, and am not afraid to, experiment
David, I would love to post the process, next time, only because I do not want to lead anyone astray, I know you would provide us with correction where needed keeping us on the right path, I want to go thru the process again with a little more accurate information and hopefully will be able to notch the belt with this.
Tom, yes I do have the craftsman lathe same as the one Tubalcain uses in his videos, I think I would be able to get the info I need from the u tube videos and books which by the way I need to find that machinist handbook. WilliamDecember 29, 2013 at 11:51 am #54354William,
Whenever I cut a thread the first thing I did was calculate the dimensions of the thread form. Much of this information can be found in MACHINERY’S HANDBOOK under threads. The thread you cut is called a 60 degree thread. This refers to what is called the included angle. The included angle is the angle between the two sides of the thread walls. One half of 60 is 30 so that is the angular path you want the cutter to follow when you are feeding the tool into the shaft. Your ATLAS LATHE and any true engine lathe has a compound axis that is to be set to 1/2 of the included angle of whatever thread form you are cutting. There are exceptions to this such as a Butress thread but don’t be concerned about that right now. Since the thread is a 60 degree thread, the cutting tool needs to be ground to that angle. The least expensive way to do this is to use at tool called a 60 degree center gage and a bench grinder. Enco sells these tools: 615-6300, 326-1096, 890-1357, 240-0228. They are inexpensive tools and are extremely helpful to grind and set up the thread cutting bit. The tool looks like and arrowhead with notches cut into it. The idea is to grind your tool bit and check the angle by putting the bit into the notch to make sure it matches. When this is done and your part is in the lathe, the tool is placed along side of the part and the bit is adjusted until it fits perfectly into the notch of the tool. once this is done, the tool is locked down. When cutting the thread, the tool is advanced into the work with the angled compound axis. The X axis is used only for positioning. For a simple screw or bolt, the thread depth can be checked with a nut. For more critical work, thread wires are used.
davidDecember 30, 2013 at 6:42 am #54355Thank you David, today I am going to order that tool, also a machinery handbook, several used ones on ebay but early dates, are the newer editions containing any more info that I would need than the earlier dated ones? A fair condition used 50 year old book if fine with me depending on the cost. I had matched up the cutting tool with the original threads, NOW I understand that most threads have the 60 degree thread, or 30degree included angle (I was unaware that most threads were like this). One thing I did not do is grind a flat on the tip of the cutting tool, I think this information on the size of the flat would be in the handbook. have to go for now, thank you, William
December 30, 2013 at 7:36 am #54356William,
Any copy from the mid 1960s on up should be just fine. Mine has some information on the slide rule so I am sure that the newer versions have removed this section. The included angle is the angle included between the sides which is 60 degrees. The flat you are refering to is called a truncation. This is only on the top of the thread not the valley so do not grind a flat on your cutting tool. The truncation provides clearance between the external thread and internal thread (bolt and nut) to allow a tighter fit without jamming.
davidDecember 30, 2013 at 8:27 am #54357Hey David,
I think William may be referring to the theroretally perfect thread where a flat (or radius) is cut into the valley of the thread. In normal home type machining practice William this is usually considered unnecessary and a sharp 60 degree pointed V shape cutter is used. Main reason is that the dimension of the flat will change with each thread pitch and diameter. I think it’s like 1/8 the pitch of the thread (not sure so someone please correct me on that one). That’s a lot like the helix angle which also changes with pitch and diameter. The flat or radius is important when the thread must be exact but in most home and basic machining applications it’s often considered unnecessary and overlooked and as David suggests just truncating the threads a tiny bit will take care of any friction using the sharp tip would cause. I’ve got a good link somewhere to a site with an online calculator for calculating the helix angle and flat if you would like it William. It’s on my other laptop so I’ll fire it up in a bit (after breakfast!) and will post it up here for you.
On a side note it’s not a bad idea to grind a tiny radius at the end of the tool with a stone to help keep the cutter from dulling or breaking and to relieve stresses that the sharp angle will leave at the root. This can help keep the part from cracking at these sharp edges – especially if heat treating the part.
I’ll be back with that link (if I can find it) in just a bit.
BobDecember 30, 2013 at 8:52 am #54358Here you go William,
Doesn’t look like it covers the flat though…just the helix for the different types of threads. I’ll try to locate info for the flat for you.
http://americanmachinist.com/thread-cutting-values-calculator
BobDecember 30, 2013 at 9:07 am #54359Bob,
You are correct. The American National and Unified Screw Thread Form has .125 x pitch for the top of the thread and .250 x pitch for the valley. This will increase the strength of the bolt slightly but unless the bolt is being pushed to its maximum strength limit it is another issue to worry about when grinding the tool. This is expecially true eyeballing it with a bench grinder. I have a single lip cutter grinder and can accurately grind a threading tool with a .250 x pitch perpendicular to the cutter with the proper clearance angle. In practice for almost all general applications, especially grinding the tool by hand, I have found that a pointed tool works fine.
davidDecember 30, 2013 at 11:44 am #54360What I had heard was the flat will also help from the tip of the cutter breaking and causing it to not cut as well as Bob has mentioned. So after cutting the threads to get what you mentioned @david pierce wrote:
truncation provides clearance between the external thread and internal thread
would you just run a file over the top of the threads? or does this occur with proper calculations in total circumference and the bottom of the thread circumference (the proper terms escape me) leaving the truncation? If this is so then I would have to make the total circumference smaller (wholly cow I am thinking too much). Also since I had cut these threads between centers I was unable to determine whether they would work or not (my by gosh and by golly method), I am assuming the thread wires would show me this. Hey I bought the 60 degree center gage from enco, I think it was in the middle of the road in price (around $8 or $9) I see how helpful this little tool will be for grinding the cutting tool and setting up perpendicular to the work piece. I also found someone selling a machinery handbook in the area, 28th edition in new condition for $40. Have to study more on finding the flat. I am not sure why I am getting so excited about all this, maybe I am going crazy or something. William
December 30, 2013 at 12:16 pm #54361Hi William,
You can do some simple calculations but it’s usually just a matter of topping off a little. Unless there are certain class tolerances to adhere to often an arbitrary choice for most practical machining purposes. Take a look at the link below. This will give you an idea of what’s happening. Don’t worry about the dimensions that it shows. The pic is just to help visualize what’s going on. You see that clipping off the thread tops still allows for the side walls of the thread to make contact and do their work without much loss in strength. You can see in the pic that putting a small radius on the tool tip will decrease the depth of the cut. The greater the radius the more shallow the cut. If the internal thread is cut with a tool with a radius and the screw isn’t topped off a little then there will be some interference between the two.
Also the advantage of turning between centers is that you can remove and replace the part with repeatability. You can remove the part, check the fit and then replace it between centers.http://en.wikipedia.org/wiki/File:ISO_and_UTS_Thread_Dimensions.svg
Hope this helps William,
BobDecember 30, 2013 at 1:16 pm #54362Hey Bob, that helps, thank you
December 30, 2013 at 1:54 pm #54363The calculation to determine the amount of tip removal of the threading tool for a 32 TPI thread is:
((((1/32) X (1/2))/((Tan(30))) X (1/4))=.0067. This is about the diameter of 2 human hairs. -
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