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Adjusting Gears Just Right

 

Bret,
I got frustrated?with adjusting the change gears a while back. and conceived?the design shown in the attached PDF.
I have posted this before.
Regards,
John Mattis (retired mechanical?engineer)



On Thu, Dec 7, 2023 at 1:46?PM CBJessee-N4SRN <cbjesseeNH@...> wrote:
The LMS 7x16 manual says ¡°?Proceed to move the shaft carrying B and C and the adjuster 'A' so that all gears mesh correctly, then tighten the adjuster securing nuts. This may take one or two attempts but make sure there is as little backlash as possible without being over-tight, (Turn the spindle by hand to test for backlash).¡±

If I just press the adjuster firmly up by hand and tighten the nut, the lathe seems to make a gnashing sound - is that what ¡°over-tight¡± sounds like?

BRET

Change Gear Adjuster.pdf
Change Gear Adjuster.pdf

 

Yeah, probably too tight. The plastic gears also tend to have tight and loose spots. When I was using them I set like I did back when I raced RC and slot cars. Use some news print. Put two thicknesses between the gears and hold them firmly together but not super griped. Tighten the adjuster down and remove the paper. You should be able to feel a little movement between the gears when it is set.?

Ryan?
On Dec 7, 2023 at 5:04?PM -0500, John Mattis <john.mattis@...>, wrote:

Bret,
I got frustrated?with adjusting the change gears a while back. and conceived?the design shown in the attached PDF.
I have posted this before.
Regards,
John Mattis (retired mechanical?engineer)



On Thu, Dec 7, 2023 at 1:46?PM CBJessee-N4SRN <cbjesseeNH@...> wrote:
The LMS 7x16 manual says ¡°?Proceed to move the shaft carrying B and C and the adjuster 'A' so that all gears mesh correctly, then tighten the adjuster securing nuts. This may take one or two attempts but make sure there is as little backlash as possible without being over-tight, (Turn the spindle by hand to test for backlash).¡±

If I just press the adjuster firmly up by hand and tighten the nut, the lathe seems to make a gnashing sound - is that what ¡°over-tight¡± sounds like?

BRET

Attachments:
 

I should have noted - I have just upgraded my LMS 7x12 with a 7x16 Bed Extension and find the gnashing is actually Gear B just barely contacting behind Gear D on it's back edge. The gears have ~2/3 engagement, likely due to problems noted below.

My Left Lead Screw Bracket is a bit beyond flush with the left edge of the bed casting and my Change Gear Adjusting Stud might not be quite located properly. LMS instructions are "On your original bed way casting, measure the distance from the front edge to the center of the hole for the change gear adjusting stud. If it is over 21/32" or less than 19/32", use the dimension you measured instead of 5/8" in the step above." My stud was 0.5" set back on my 2013 model LMS 4200 7x12, so I went with 0.5" as indicated.

I'll get a picture when home again and post - sorry if I'm not describing it well. I'm hoping some tweaks might help fix the issues. At worst, I can grind back the read edge of the 80-tooth Gear B. :-(

Trying to precision drill holes in the bed casting proved quite difficult, even with a drill guide.

BRET
 

I read somewhere (don't remember) that if you use a slip of thin paper (newsprint works well) between the gears, that is the clearance you need. You crush the paper as you mesh the gears and tighten. Then you had turn the gear train by hand to get the paper out and then put some grease on the gears. That is how I put the banjo to mesh on my lathe...

On Thu, Dec 7, 2023 at 1:46?PM CBJessee-N4SRN <cbjesseeNH@...> wrote:
The LMS 7x16 manual says ¡°?Proceed to move the shaft carrying B and C and the adjuster 'A' so that all gears mesh correctly, then tighten the adjuster securing nuts. This may take one or two attempts but make sure there is as little backlash as possible without being over-tight, (Turn the spindle by hand to test for backlash).¡±

If I just press the adjuster firmly up by hand and tighten the nut, the lathe seems to make a gnashing sound - is that what ¡°over-tight¡± sounds like?

BRET


--
Buffalo John
 
Edited

? Here's that gear problem picture. Adding an M8 washer on the Stud moved Gear B off contacting the Left Bracket and gears engage more - is that a reasonable solution?
 

Like the pdf how complex it can be .
The way I found is paper between the gears on setup. It fast and easy.?
Most gears like a gap of 0.005" [0.12mm] .
You adjust the paper layers till gears run quite.?
Today I can feel the gap need.

The 0.005" [0.12mm]?gap is only for most change gears in machine shop. Larger gears needs a greater gap and watch gears need a lot less. But here we do not care we are working with mini lathes.?

Dave?
 

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It's pretty common on these lathes to have the? lead screw bracket's mounting wonky .A lot of folks have had to re drill/enlarge the screw holes to get things lined up .

animal

On 12/7/23 4:03 PM, CBJessee-N4SRN wrote:

I should have noted - I have just upgraded my LMS 7x12 with a 7x16 Bed Extension and find the gnashing is actually Gear B just barely contacting behind Gear D on it's back edge. The gears have ~2/3 engagement, likely due to problems noted below.

My Left Lead Screw Bracket is a bit beyond flush with the left edge of the bed casting and my Change Gear Adjusting Stud might not be quite located properly. LMS instructions are "On your original bed way casting, measure the distance from the front edge to the center of the hole for the change gear adjusting stud. If it is over 21/32" or less than 19/32", use the dimension you measured instead of 5/8" in the step above." My stud was 0.5" set back on my 2013 model LMS 4200 7x12, so I went with 0.5" as indicated.

I'll get a picture when home again and post - sorry if I'm not describing it well. I'm hoping some tweaks might help fix the issues. At worst, I can grind back the read edge of the 80-tooth Gear B. :-(

Trying to precision drill holes in the bed casting proved quite difficult, even with a drill guide.

BRET

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