LMS Mini Lathe Feed Rate - Vary Gears?

[VicHobbyGuy]

Both Steve Aylor and Kwick Aronson sell slow feed gear sets for the 7x lathe. You can find them over at the 7x mini lathe group on Facebook.
Kwick Aronson's gears also are sold by LittleMachineShop. I've dealt with both of those guys and service was excellent. And the gears definitely work to give a better surface finish.
https://littlemachineshop.com/products/product_view.php?ProductID=1137&category=

BTW, if you have a 7x lathe the greatest concentration of users is in the Facebook group. The old Yahoo group - now at https://groups.io/g/7x12MiniLathe is also a good resource.

 

[strantor]

You maybe able to swap the gears around in an unconventional manor to obtain the feed rate. Unconventional simply means putting the gears in a configuration not described in the manual. Lathe manuals usually only provide a very few of the possible threading or feed rates that are possible.

I have posted an Excel spread sheet workbook that can be configured for almost any lathe gearing and it will then by using pull down menus to describe the gears at the various locations the feeds and TPIs appear in other cells of the spread sheet. I did this first for my PM1440GT, but later I added other sheets for other lathes, but simply copying the sheet and then changing the gears. We can probably do this for your lathe if you can provide a manual and some other descriptions from the lathe. Do you have a manual? If so post it. The really powerful part of the workbook is that I wanted to learn to write Excel macros so I did. There are several very useful macros that run the lathe sheet of your choice and then generated a list of ALL Possible gear position results. Other macros allow you to search this sheet for the exact value you want or for close approximations to the value. There are other macros for sorting the lists etc.. There is a sheet in the workbook with extensive Readme notes.

You can get the workbook at the link below or directly download the work book at the following HM URL . https://www.hobby-machinist.com/attachments/tpi_manylathesrev1-nb06_2023-zipped-zip.465427/

It is zipped because HM does not allow workbooks containing macros to be posted. Zipping the file hides this from the HM and allows it to be posted. Since I wrote the macros I know there is nothing harmful about them. In fact if you keep your Excel program set up so that it asks you before you enable macros you can look at the text file of them and see they are safe to run.

If you post the manual, a list of the gears, possibly some photos of the gear locations... that you have and which axles they will fit on .... I can take a look at generating the excel sheet for your lathe... or you can do it and I can answer questions. My guess is that your lathe does not have a gear box, only external gears? In this is the case, it is quite easy to set up the spread sheet. It is probably similar to the sheet I created for the PM1130V lathe. However, the number of gears listed in this sheet needs to be reduce as it is way to large to run the macros on. Doing so will take way too long.



Dave L.

This is the same approach I took for cutting 42mm (0.61 TPI) on my Logan.

I also made a spreadsheet but mine doesn't use macros; just formulas in columns. Do your spreadsheet macros generate gear pairs to achieve a desired pitch? Because mine lacks that ability and it was pretty time consuming working the problem from the other end, manually plugging in numbers over and over and over until I finally found something that was acceptable. If yours doesn't have that limitation then I need to look under its skirt. I would be looking at it right now if I wasn't posting from my phone.

 

[homebrewed]

I was not trying to interfere, just trying to help out. I went to all of the trouble to built that workbook and though it might be helpful.
I do not know this lathe nor its gearing or gear arrangements. That is why I requested the manual/pictures/etc. I found a very poor quality photo of the front of the machine and could not see a gear box, but no manual. So I assumed that all gearing changes occurred at the external gears. But I found no picture of these external gears nor their arrangement. But I assumed there would be at least a banjo to form a center axis. If not then all one can make are the ratios of the two gears sizes, where the gears are attached essentially to the spindle and to the lead screw directly. I would agree with you that the simplest thing is to use a 3D printer to make other gears, but a 20T gear is pretty small to maybe cannot be made any smaller? It also sounds like an 80T is pretty large on this lathe so is there physically room for a larger gear than 80T. He ask if he could halve the rate so that would mean that the gear would need to be twice as large 160T. Since the diameter is proportional to circumference and the tooth size is a constant that would mean that the 160T gear would be twice the diameter of the 80T gear. You said remove the cover, but is even that going to be sufficient? I would still be interested in seeing a manual and picture of how the gears physically mount to the machine.

Having said all of that, if there are some gear arrangements which have not been listed in the manual the spread sheet could quickly generate the complete list. This might be handy for non-standard threads. It would be trivial to set up the spread sheet by just setting the transpose gears to a ratio of 1. But one still needs to know what gears are available.

Dave L.

It wasn't my intent to chastise you for "butting in", and if I came across that way I apologize. In turn I was just trying to clarify the situation for this class of lathe.

As far as the change gear setup goes, the lathe can accommodate up to 4 active gears, but some configurations actually only use two. Full disclosure: I haven't tried any gears with more than 80 teeth so I don't have any direct experience regarding the largest-possible gear(s) for these lathes. Just to make things even more complicated, the OEM banjo places additional limitations on gear combinations that can actually be used (due to fitment problems). That limitation is specific to this class of lathe. To be specific, the four gears are given as A, B, C and D. Any case where B > (C+D) is illegal because the gears will interfere with each other.

The change gear calculator found here: https://littlemachineshop.com/reference/change_gears.php should help clear things up. After entering a desired TPI value and hitting "enter", additional information comes up which shows the actual change gear setup. But that program hides the B > (C+D) limitation.

 

[strantor]

Just to make things even more complicated, the OEM banjo places additional limitations on gear combinations that can actually be used (due to fitment problems). That limitation is specific to this class of lathe. To be specific, the four gears are given as A, B, C and D. Any case where B > (C+D) is illegal because the gears will interfere with each other.

That is what I encountered when trying to hit a non-standard pitch on my lathe and I was able to work around it by using one pair of gears in the standard diametral pitch of all the gears on the lathe, and a second pair of gears with a larger diametral pitch.

 

[B2]

Here’s that manual and the pic/chart for gearing https://littlemachineshop.com/products/product_view.php?ProductID=4924

The default 0.004”/rev is ACBD 80/20 gearing.

Thanks I will take a look tomorrow in the light of day. I will say that the end of your lathe does not look much like mine. Nevertheless, it is all about ratios between gears. However, physical layout can limit what can be put where.

 

[B2]

Anyway, I bought a speed control, a Dell laptop power supply, and a drive motor, which looks a little like a car wiper motor.

This lathe maybe an ideal candidate for an ELS system. It would make life a lot simpler.

 

[B2]

I also made a spreadsheet but mine doesn't use macros; just formulas in columns. Do your spreadsheet macros generate gear pairs to achieve a desired pitch? Because mine lacks that ability and it was pretty time consuming working the problem from the other end, manually plugging in numbers over and over and over until I finally found something that was acceptable. If yours doesn't have that limitation then I need to look under its skirt. I would be looking at it right now if I wasn't posting from my phone.

My spread workbook contains a number of sheets, each dedicated to a lathe model. Each of these are laid out in the same format so that it is reasonably to add more lathe models. One just inserts a new sheet in the workbook , then copies a previous lathe sheet and pastes it into the new sheet, followed by modifying it to be for the new lathe model. Once this is done you see a number of columns for handles/knobs on gear boxes if you have gear boxes. To the right of these are a number of columns representing the various external gear axles in an order that the gears would touch each other. At the far right is the spindle gear, at the far left of these next to the gear box is the gear on the gear box shaft, in between theses are the columns representing the inner axles or banjos. I have it set up so that there could be 3 banjo axles. At the top of these columns are pull down menus that select the gears that are be low this. Above all of this are the calculations of ratios which are multiplied in a row across the columns of ratios. The final TPI and feed rates show up on the very far left and the metric version of these number are at the very far right side. So you just use the pull down menus to select a gear for a given position and the resulting calculation appear.

There is a fundamental macro which simply causes all of the pull down menus to step through their paces. Each time a gear is selected by the macro the results of the calculation is saved as a line of info on a separate spread sheet. The next gear result in placed on this same sheet one row down. This repeats over and over until all possibilities are completed. Hence one gets a single sheet which contains all of the possibilities of gear combinations. Depending upon how many columns (axles) one uses and how many possible gears could be on each axle one can get a very large number of possible thread values. I think I call this list sheet something like AllTPI. On my PM1440GT this number of possibilities can be 20K to 30K. If there are a lot of possibilities it can take a while to generate this table, but you only need to do it once..... unless of course you add a gear value to your set.

Other macros can sort the order of the rows by one or multiple columns. Others can search the columns for specific or approximate values. For example you might sort the list by the TPI column, followed by searching the list for a TPI value such as 13.5? (or say 13.50?)and it would find all of the TPI values in the table which had a value between 13.5999 to 13.4001. These search results are inserted at the top of the sheet AllTPI in the order that they were found. There is another macro which will transfer these searched results to a separate sheet. There is yet another macro which will step through all of the standard thread sizes and generate a search for each of them. Hence you can make a table of all of the possible ways to make all of the possible standard thread sizes and their approximations (your choice). There are other macros which are listed in the Readme sheet. There is a macro which will hide or unhide columns in the sheet so that you can print the sheet without having to view everything that is being generated. There are even macros for cleaning things up and deleting sheets which have been created by the macros. I included 13 macros. The macros have a few interactive question windows to allow the user to make choices. For example the Macro that generates the AllTPI list asks the user which of the lathe sheets is to be used in generating the list. When one runs this macro it deletes any sheet which does not have a name that starts with the letters "uw". So once you generate some information and you do not wish to loose it you simply change the sheet name to i.e. uwAllTPI.

So the only real way to understand the power of this workbook is to use it. Try it out. https://www.hobby-machinist.com/attachments/tpi_manylathesrev1-nb06_2023-zipped-zip.465427/

Let me know what you think.

Dave L.

 

[Firstram]

The finest "threads" you can cut with the stock change gear set is 256 TPI, which produces the .0039" fine feed. You have to use both 20 and 80-tooth gears for that. The gears produce a 4*4 = 16:1 relationship between the spindle and lead screw, which is 16TPI. 16*16 = 256, so end of story, you don't get any better than that.

To get a finer feed you will have to either print some additional gears or take the Varmint Al approach. In the former case, you may have to remove the gear cover to accommodate the larger-sized gears.

There also is a fine-scheme approach that uses a different gear "banjo" that you have to make. Information on the fine-feed banjo can be found on https://groups.io/g/7x12MiniLathe/files/Richards folder, but you may have to become a member to access the file. It is claimed to produce about a factor-of-4 improvement over the standard banjo. I think that assumes using nothing but the standard gear set so it should be possible to achieve an even greater improvement if you use printed gears. However, if you take that route the banjo probably will have to be redesigned to accommodate the larger-diameter gears.

I am using this setup on my 7x, it works great.

 

[MaverickNH]

I am using this setup on my 7x, it works great.

It can, yes! I had observed that some “larger” mini lathes had autofeed gearing selectable down to 0.002”/rev - that’s why I raised the question. With 0.004”/rev, other steps can be taken. The stock HSS indexable tools LMS sells come with 1/64th radius cutters, but they also sell 1/32nd radius cutters that would have more overlap between revs for a given DOC, but at greater tool pressure. It certainly easier to use a wider cutting tool and reduce DOC for my hobby needs than rig some complex and expensive solution.

As a newbie, I didn’t know if there were other cheap/simple solutions, so asked here and learned a lot from the forum members - many thanks!

 

[WobblyHand]

It can, yes! I had observed that some “larger” mini lathes had autofeed gearing selectable down to 0.002”/rev - that’s why I raised the question. With 0.004”/rev, other steps can be taken. The stock HSS indexable tools LMS sells come with 1/64th radius cutters, but they also sell 1/32nd radius cutters that would have more overlap between revs for a given DOC, but at greater tool pressure. It certainly easier to use a wider cutting tool and reduce DOC for my hobby needs than rig some complex and expensive solution.

As a newbie, I didn’t know if there were other cheap/simple solutions, so asked here and learned a lot from the forum members - many thanks!

Just remember, that for a non rigid lathe like a mini larger radius cutters are more prone to chatter. HSS is an answer. Another answer is ground carbide, ie inserts for aluminum, even though you are cutting steel. I use TCGT inserts most of the time, except for rough work. I've been able to get near mirror finish on aluminum and almost as good on good machining steels, like 1215, 12L14, and 1144. On both my mini 7x16 LMS lathe and my G0752Z 10x22.