TPI Feeds X-Feeds: Generalized Excel file for your Lathe

[B2]

TPI Feeds X-Feeds: Generalized Excel file for your Lathe​

Hi Folks,

My PM1440GT lathe manual only showed a few of the possible threading values and it appeared to me that the Feed rates were incorrect. They were. Hence, I set about to figure out what all possible TPI could be achieved via both the LeadScrew as well as the feed bar. The process became more of a project than I had intended but I finished it up some time ago. Then it occurred to me that the Excel work book that I had created might be of interest to to others so I extended it to a few other lathes and made it more general. With the help of others, especially @Ischgl99 , @Provincial , @jbolt , @davidpbest , @ptrotter, @aliva and many others I have gone a head and added other lathe models to the work book. For reference, I even added @jbolt's spread sheet for the 1440GT and DavidPBest's table of metric threads for the PM1340GT. Others have expressed interest in the same topic so I will list some of them to provide them with a link: @Dpaul7 @GunPlumber , @BROCKWOOD

So this it how it works. I created a template based upon my PM1440GT gear boxes, external gears, and Feed and X-Feed apron gears and gear ratios. I then copied this and modified it to created templates for some other similar lathes that folks had volunteered information on: PM1340GT, Atlas618, JET-BDB1340A, MMLB-Norton, (MetalMax), and MM1340LB-Lever (MetalMax) versions. However, the template is general enough that it could probably be useful to most any lathe. This template uses pull down menus to select the gear box lever positions and the external gears that are available (determined by the user) to show a resulting TPI, feeds, etc... in both English and Metric units. I then wrote some macros for the spread sheet which generate a table of all possible gearing combinations and the resulting TPI, etc.... In the case of my PM1440GT this is about 6400 possible combinations. Hence, one can probably make most any thread that he might need or at least a very close approximation to it. I then wrote some more macros which will automate the search to find the gears needed to find these TPI,, etc values. Of course, I also needed a macro to sort, and organized the table .... so more macros.

Of course, this also allows to you put in gears that you are thinking about purchasing, or making, to see what new TPI values would be generated. Or you can just print out the table and have an extensive reference. I noticed that some folks do not have gear boxes, only external gears on their older lathes. This workbook should be very helpful in deciphering all of the possibilities.

So, I think the attached Excel workbook will generate the TPI for all possible gears of your lathe too... if you are willing to work at little to copy and modify one of the templates to match your lathe. I would even be willing to assist in this process if you like.

There are three attachments: 1) The Excel workbook with built in macros that has been zipped so that HM will allow it to be posted. 2) The same workbook, but with the macros left out. (Not as valuable as it only allows you to view the sheets and not use the power of the macros.) However, you can get an idea of what a large table looks like at sheet tab "AllTPI". 3) Finally there is a zipped file which only contains about 7 useful macros. This allows one to examine the Macros with almost any text editor ( I prefer NotePad++ which is free via download) to ensure that they contain nothing malicious. One can then import these into the workbook of item 2 to give it functionality. Macros are mostly just text but the extension is .bas file and some text editors will not open these. Just change the extensions to .txt and then NotePad will open them. But the .bas versions should be the ones that are imported other wise the KeyStroke command maybe lost.

There is a Readme sheet to explain how things work and what the macros actually do. I had thought I would create a couple of more macros which would pull out all of the standard English and Metric thread values as well as those that are close approximations, but I just have not gotten around to it. Maybe someone else will add this. Anyway, there is a search macro which will find a specific or approximate TPI for you quickly. There are also multiple sort macros so you can sort by almost any column in the table.

I wrote the workbook using Excel 2010 so it should be old enough that it will be compatible with newer versions of Excel.

Please let me know what you think and how I can help... if needed. If this proves to be useful perhaps the number of templates will continue to increase.

To get started Use the Readme sheet(tab) in the workbook... or if you installed the macros, just use the Key Strokes: Control+Shift+G to generate a large TPI table. Be patient as it calculates, there can be a lot of lines in the table. You can watch the progress message via the lower left hand corner of the Excel work book.

Dave L.

PS. I used my high precision counter and DRO on my lathe to get the accurate Feed and x-Feed rates for my PM1440GT. Described here:

VFD conversion using solid state electronic components.

The forum about the feed rates is here:

I have a PM1440GT and it says on the front gear panel that the ratio of the Power Feed and the X-Feed rates are simply 2:1 (or 1/2) . I think this is the common statement made for many lathes. However, I have made a quick attempt to measure these rates on my machine and I get a number more like 3.14:1 not the factor of 2. I think the x-feed part of the table on the lathe is incorrect.

 

[B2]

By the way, while I am fairly certain of the accuracy of the workbook for the PM1440GT and the PM1340GT, I am less confident for the other lathe models.... especially the feed rates and the common external gears. So if you have one of these other lathes, please check out the workbook sheets for these carefully so that if there are errors we can correct them.

Thanks
Dave L.

 

[Provincial]

Nice work Dave! Thanks!!!!!

 

[Gingersnaps]

Super useful! Thank you so much for putting in the time to create a tool for others to use.

 

[B2]

Hi @Provincial
We have bounced this conversation around several threads, but I think this is the most appropriate for determining TPI. You are correct that it did not belong in the thread :

MAGNETICALLY ACTUATED GARBAGE DISPOSAL

Yes, we could continue on:

X-Feed rates on their PM lathes

but that conversation was more about feed rates than TPI.

Your lathe: Metal Max with Norton Gear box (my Excel Work book Spread Sheet name: uwMMLB-Norton).

Please provide me with list of the external gears that you have available.

I determined that that gear position C-6 is 1.0 mm lead when using a 40-tooth gear in both the upper and lower positions of the banjo drive. To get 1.25 mm, I need to speed it up by a factor of 1.25, and by changing the lower gear to a 32-tooth one, it speeds up the quick-change input by that amount. I can get a 32-tooth gear from Grizzly for their G9249 12 x 37 lathe which I hope will fit, or at least can be modified.

Your analysis for the 1.75 mm pitch agrees with my conclusion that I can use the B-6 position. The thread chart says that a 40-tooth upper gear and 40-tooth lower gear gives 2 mm pitch in that position. With a 30-tooth upper gear, it gives 1.5 mm pitch. To split the difference and get 1.75 mm pitch, a 35-tooth gear in the upper position should work perfectly. This agrees exactly with your calculations.

I'll have to verify the modulus for these gears and then look for a source. The upper gear has no hub, is 10.3 mm thick, has a 16 mm bore and a 5 mm keyway.

We can continue this discussion on the old x-feed rates on PM lathes thread, which is where we originally started this discussion.

--- Yes, the spread sheet found 1mm/thread at C-6 40/120/127/40 (gear box to spindle).
--- Yes, the spread sheet found 1.25mm/thread at C-6 32/120/127/40 (gear box to spindle), it also finds 1.25 using other gears, but I'm in the dark as to what you have available.
--- I am glad the thread chart is providing guidance for the other values as well.

Please provide me with list of the external gears that you already have available so that we can see if you really need to purchase gears of if you can live with some close approximations. You may have done this in the past, but I cannot find it.

Dave L.

 

[Provincial]

I have two 40-tooth gears and one 30-tooth gear. The manual says that 40-tooth gears are used in both the upper and lower positions and the 127-tooth as an idler when using the TPI chart.

The metric threads use two options, 40/127 x 120/40 and 30/127 x 120/40. (spindle to gearbox)

I think that I will be able to cut 1.75 mm threads with a set-up of 35/127 x 120/40. (spindle to gearbox)
I should be able to cut 1.25 mm threads with a set-up of 40/127 x 120/32. (spindle to gearbox)

I'm attaching a PDF of the page in the manual with the threading charts.

I think your spreadsheet is working for this machine. It will be interesting to see if other gear options will be more practical.

Thanks!
Jock

 

[B2]

Hi @Provincial

Thanks for the images of the gear tables and for the values of the gears that you have. They certainly did not give you much to work with in the way of external gears, but I think you can get by.

I took only the gears that you have 30, 40, 40, 120, and 127 and I assumed you could put them in any order:

If you arrange the external gears as: Spindle/(30T/120)*(127/40T)/Gear box ... the order that your tables use, you will get the following ( flip the 120/127 around from what is listed on the lathe table). Gear box settings:

Spindle/(30T/120)*(127/40T)/Gear box:
1-C yields 1.26008mm. Error of only 0.01008/1.25 ~ 0.8%
5-B yields 1.75315mm. Error of only .00315/1.75 ~ 0.17%

I would think that these are close enough for almost any application and that you would not need to make/buy other gears unless you just want to be dead nuts on the 1.25mm and the 1.75mm. I suppose that if you were going to make really long thread engagements and make the threads really tight you might need to have better accuracy. Anyway you should check these settings and see if I got it right. Also, I went a head and filled out the threading tables for these arrangements.... so they are more complete than what is shown on your lathe. They are attached as well as the spread sheet versions with and without the macros. Also attached is the spread sheet using your gears.

If you have not gotten the Excel macros to run or if you want me to run some cases for you just let me know.

 

[B2]

Hi @Provincial

I just realized I left out the three tables where the exchange gear 120/127 is not used: 40/120/40, 30/120/40, and 40/120/30.

If and when I get a chance I will try to add them to the posting. Anyway, all cases including these are in the spread sheets.

 

[Provincial]

Thanks Dave!

I feel guilty for failing to mention that the "change" gears are not interchangeable between the spindle and gearbox ends. The spindle end (actually, the output gear on the tumbler) has a 16 MM bore, no hub, and is 10.3 MM thick. The gearbox end has a 19 MM bore and has a hub so the overall thickness is 19.5 MM (of which 9.64 MM is the face of the gear).

This means that the only gear I can use on the gearbox end is the 40-tooth one. I can swap 40-tooth and 30-tooth gears on the "spindle" end.

If the Grizzly gear, which comes off the gearbox input of the 12x37 lathe, is the same or can be modified to fit, I'll be able to cut 1.25 MM pitch threads.

So far, I've found a place in England which has a 35-tooth gear that is thicker, has a hub, and an 8 MM bore. This can be held by the hub, bored, and trimmed for thickness in one operation. A second operation could remove the hub and it would be ready for cutting the 5 MM key seat. It could be worse!

Thanks Again!

Jock

 

[B2]

Hi @Provincial

Well non-interchangeability and thickness differences are a bummer! On pulleys I have found that the OD of hubs are not always in the center of the rest of the part. While this may not be a big issue for thinning it would seem to require centering for re-cutting the bore. My SB10-Heavy uses a spacer ring rather than a hub.

If you do not wish to cut your own I think would seriously consider a 3-D printed gear. There are several folks on HM besides me who have a printer or who have made gears. There are others out there on the web who sell these. I googled "lathe change gear set for sale" and got lots of hits. One in particular jumped out at me. https://farmboysales.com who seems to both make and sell steel gears as well as 3D printed ones. He also sells on ebay as do others.

I am not for sure it is possible to do so, but if so there is the option of flipping the 120/127 and using the 30T at the spindle to get a close approximation (<1% error) to 1.25 and 1.75. The arrangement is below.

Good luck in which ever direction you choose to go.

Dave L.