What thread is that??

[iron man]

I was looking into modifing my Grizzly mill and was looking at the threaded lead screw that is common on most of these imports the thread is 16 TPI and at first glance appears to be an acme type thread but on closer look it is nothing more than a regular thread with the top point knocked off. The pitch is the same as a normal thread and the base of the thread is still pointed but the screw and the nut both have the point squared off. I suppose they did not want the point to roll off and become jammed but I am just guessing. An Acme thread would not be near as fine but I would think it would stop a lot of backlash I may look into this but there has to be something better. Ray

 

[Wheels17]

I just bought a G0704, and an Enco lock-down vise. The vise appears to have the type of thread you mention. It looked funny to me when I first looked at it, but assumed it was just my bifocals. I can't take a good look right now, as I don't want to tear down my current tooling setup.

I did look at the X traverse screw on the table, and the Z screw for raising the head and they both seem to be Acme-ish threads. Flat tops and bottoms of nearly equivalent width, and a much shallower angle than 60 degrees on the flanks of the thread. The table thread has to be 10 threads per inch, as one turn of the dial gives .1" of table movement(no DRO yet, still counting turns).

In general, the mill seems pretty satisfactory. The dovetails are nothing to write home about, but the machine seems to function well. The headstock seems to be well aligned in the Y direction relative to the column, and it was easy to get the X direction parallel to the column. The head came from the factory with the 3-bolt modification. Tramming the column in the X direction went well, but was surprisingly sensitive to the bolt torque. I'm making little rectangular parts and I can hold .001 end to end on a 1 1/2" part when milling in the X direction.

The Y direction has problems. The table holds .0005 under the quill using a dial test indicator as it is moved in the Y direction, but tramming the column shows .0045 across the table. E-mailed Grizzly, and the spec is .005 or better...... Have to finish the little job I'm working on where this inaccuracy isn't important and will work on shimming the column when my shim pack arrives from Enco.

 

[iron man]

I have the GO727 nice little mill I would like some more head room between the table and the collet so I am making a column extension with a long and larger lead screw I just thought it was kind of funny they try to make it look acme'ish and it is nothing more than a common thread. I will post pictures when I am done.. Ray

 

[DMS]

Maybe I'm not understanding the question, but you can have an ACME screw with the same pitch as a normal machine screw. The difference is the angle of the threads themselves. Typical machine threads are 60 degrees, acme are 29 (14.5x2) degrees. Tops and valleys are flat.

There is a metric equivalent, threads are 30 degrees. You sure it's not ACME?

 

[iron man]

It looks like a regular thread with just the point cut off the pitch is 60 degree and not 29 or 30 I have cut a lot of acme threads in the past and this one is made to look like an acme thread at first glance but in reality it is just a normal thread with the points knock off how else would you get a 16tpi and still have it be acme there is not enough room between threads and the thread would be thin and weak. This is very common on most of the mini mills and lathes I have seen... Ray

 

[DMS]

Machinery Handbook does say that 16tpi ACME is standard (though that's the smallest they list). You're right though, if it's 60deg, it's something else. It would be very unusual though, as 60degree threads are not normally used for power transmission.

 

[iron man]

It is easyier and more common but I agree I like the acme thread better but 16tpi would seem awful tiny width thread. I got out my jewelers glass and it does appear as though they tried to cut and acme thread but the nut it screws into is without a doupt a common thread. A regular thread depth is twice as deep as what they have here this cannot be very strong with a thread depth less than 20 thousands its going to change now.. Ray

 

[Ulma Doctor]

i had the same question on my hf 7x12, my leadscrew appears to not be acme, but a crappy machine screw thread with the top knocked off it. it is not a good way to transmit power, no wonder why the leadscrews wear quickly. i have painstakingly adjusted just about every aspect of that lil devil including remachining the leadscrew bracket mounts so i could make the half nuts apply better. they really screwed the pooch in that area...hopefully i can keep a leadscrew in it for a minute, but if not i'll just have to upgrade somehow

 

[iron man]

i had the same question on my hf 7x12, my leadscrew appears to not be acme, but a crappy machine screw thread with the top knocked off it. it is not a good way to transmit power, no wonder why the leadscrews wear quickly. i have painstakingly adjusted just about every aspect of that lil devil including remachining the leadscrew bracket mounts so i could make the half nuts apply better. they really screwed the pooch in that area...hopefully i can keep a leadscrew in it for a minute, but if not i'll just have to upgrade somehow

My grizzly is a knee mill and I just made a long lead screw for it because I plan on making a column extention when I am done instead of 6 inches of clearance between head and table I will have 12" so I increased the diameter of the lead screw as well because there was room and it just seemed like a good idea. For some reason it has made the table seem more stable I stayed with 16tpi and some day I will change that as well but this was an unexpected big improvement plus my parts and threads fit better.. Ray