Threading at 400 RPM

[uncle harry]

Hello Larry, the bearings used for the idler gears are not critical. I simply chose gears based on the diameter and width that were prelubed and sealed. The bearings need to be narrow enough so that you can leave a shoulder between the two bearings which is needed to keep the gear in position. The specific bearings I used were on hand and had been originally purchased for my band saw guide. Like I said, not a critical item.

I do not work much with cast iron so I am not the one to ask about the bearing qualities of the material. Making the bronze inserts was not difficult and they have proven to be very reliable and provide smooth shifting from forward to reverse.

Mike, thank you for your kind comments but this project is not as complicated as it first appears. Gray Meek did the heavy lifting I used his creation (the compact dog clutch) and adapted it to the G0602.

Jim

Regarding choice of bearings: Igus (brand name) makes plastic bearings that outlast oilite type bronze bushings in agricultural enviornments by a factor of 9X.

They are self-lubricating & come in various specific formulations for various applications. I have used them for building special machinery & I would not hesitate using them for this application. McMaster-Carr offers similar plastic bearings as well.

 

[rwm]

Brilliant! Looks complicated to execute.
R

 

[JimSchroeder]

Uncle Harry thanks for the tip on plastic bearings, Using those could eliminate the need for the oil port and a periodic oiling.

Jim

 

[Baithog]

Parden me for being a pest, Jim.

I have materials on order, but they are out of something. I received the tooling I needed... well I received the torn open package in a plastic bag with a note from USPS that they had a problem with it. Nothing was in the package, so that is being reshipped. Not a fortuitous beginning.

I have occupied myself with transferring the magazine drawings into Turbocad so that I will have easily replaceable drawings. I considered making the copies available to others here, but there is that thing about copyright and the need for HSM to make enough profit to keep serving us such great projects... beside, its really hard to duplicate your results without having the article's text.

And now for the pestering. There appears to be an oil groove in the main axle with a 'see text' note on the drawing, but I don't see mention of the groove in the text describing the oil passage.

The outer axle appears to run on the outbord end of the main axle. The main axle at that point is dimensioned as 0.450, but the bore of the outer axle is dimensioned as 0.437. Unless I am missing something, that isn't going to work.

I am getting ready to work on the body drawing. I am confused about the pocket depths. It will probably clear itself up once I have the gears and axles in hand, but it would have been easier if you had provided the depths in a table... maybe label the pockets A, B, C with their depths? I haven't used sketch-up since it first came out. Can dimensions be pulled of of the sketch-up model?

 

[JimSchroeder]

Hello Larry, thanks for the feedback. The following drawing may help clarify the dimensions of the main axle.



The axle is a press fit into the base so you need to take that into account when sizing the hole and outer diameter of the axle. I left over size by about 0.002" and used a bench top arbor press.

The pockets in the billet can be seen in this drawing.



I hope this clarifies things if not please let me know and I will see if I can fill in the blanks.

Jim

 

[Baithog]

Thanks. The 3D sure makes the body easier to figure out.

There does seem to be an error in the magazine. The 0.450 dimension should have been on the right side of the view in picture #9, and there is no 0.437 dimension on picture. It is a recoverable error, since the axle can be re-chucked and turned down, if the discrepancy isn't discovered until the outer axle is turned.

 

[JimSchroeder]

Hello Larry, thanks for the heads up. You are correct the magazine has the wrong dimension, not sure if the drawings that I submitted were in error or more likely incomplete. I dropped a note to George Bulliss and I am sure he will add a correction in the next issue. If you have any questions don't hesitate to drop me a note or post it on this forum.

Jim

 

[Beez]

Hi Jim!
i have read the first installment of your article with relish. It's much easier for me to understand than Graham's articles. I have his books and HSM articles as well.

I would like to modify this design to work on my Graziano SAG-17 lathe. I need to understand a few things first. For one, I presume that the gear ratios are important, between the spindle output, and the gearbox input, but none of the articles I have read make much mention of what is required. This is the biggest question for me, how to select the number of teeth on each input gear,and the forward, reverse, and output gears.

other than that, I presume it's just a matter of making the pitch diameters of all the gears tangent, with a tiny bit of clearance? I have Ivan Laws book but have never designed gear trains.

thanks for any input you may have, and thanks for the HSM article!
chris

 

[JimSchroeder]

Hello Chris, I have had a number of emails and other requests for a better explanation of how this clutch actually works. Let me try with this post.

The article published in the last issue of Home Shop Machinist outlined in some detail the construction methods for build the threading clutch. One area it did not cover is how the clutch functionally does what it does – drive the lead screw in either the forward, reverse or neutral direction. It is the intent of this post to explain how these gears along with the dog clutch perform these tasks.

The clutch assembly consists of five gears and the dog clutch. The gears allow you to select the direction that the lead screw rotates thus providing a forward and reverse motion. A dog clutch is binary positioned clutch, it is either engaged or not engaged there is no in between.

This threading clutch is essentially a series of idler gears that form two parallel gear trains. One train drives the lead screw forward and the other drives the lead screw in reverse. Idler gears only change the direction of rotation and do not change the gear ratios of the gear train. The idler gear may be of any size relative to the gear that is driving the idler or the gear that idler drives, the ratio stays the same. The dog clutch is inserted into the gear train between the spindle gear and the fiber gear that the spindle gear drives. This version of the clutch was designed for the Grizzly G0602 but is easily adapted to many other lathe designs. I will use the G0602 in this explanation.


Diagram # 1 – the original gear layout of the G0602 showing the direction of rotation while running in the forward direction. The clutch assembly will be inserted between the spindle gear and driven fiber gear necessitating the relocation of the fiber gear.



Diagram #2 – This is the gear train layout with the dog clutch gears inserted between the spindle gear and the fiber gear. The original G0602 gears are in yellow and clutch gears are red.



Diagram #3 – The second idler gear drives the first dog gear in the opposite direction when compared to the second dog gear.


Diagram 3 shows how the two dog gears are driven in opposite directions. Inserting an idler gear into a gear train will reverse the direction of the gear train that is connected to that idler gear. Thus we have two gear trains in this clutch the first is driven by the first idler gear which in turn drives the second dog gear. The second gear train starts with the second idler gear which is driven from the first idler gear and then drives the first dog gear but in the opposite direction.




Diagram #4 - shows the two dog gears rotating in opposite directions and straddling the dog clutch disk. The disk is keyed to the output shaft and when the disk is moved to the left or right it engages the a pin in the dog gear which in turn then rotates the output shaft in the desired direction.



The axle that runs through the gear assembly that contains the two dog gears and the output gear consists of two shafts co-axially located. The inner shaft support the assembly and the outer shaft is keyed to the output gear and can be driven by either dog gear or left in neutral. A shifting fork assembly moves the dog disk from one side to the other and is held with a detent.


Hopefully this adds some clarity to how the dog functions. The magazine article in HSM was focused on construction rather than operation. If you have any questions please post them and I will respond to them.

Jim

 

[Beez]

Excellent!
Very clear explanation.

So, since we are interposing additional gears in between existing gears, our new gears all factor out? I can see this with one new gear in between two existing gears, and it's mathematically obvious, but not as much with a whole new gear train in the middle.

If this is true then it really doesn't matter how many teeth each gear in the clutch drive has, it's just a matter of convenience and making things fit? Somewhere in the many threads on this subject I read that it's important to have a ratio between spindle and clutch >= 1:1 so that there is only one relationship between spindle and lead screw. A ratio less than 1:1 allows more than one? I get lost here.:thinking:

If the two idlers are the same, and the three clutch gears are the same, one might make a long gear and then slice it into individuals to save indexing time during manufacture.

Thanks! )
Chris