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# Which metric threads will an American Pacemaker cut ?

#### SouthBendModel34

##### Diamond
I can give you a general answer: It depends on how much access the design of the headstock allows to the gear train. If everything in the gear train is enclosed and there is no provision for the "transpostion gear" used to convert inch to metric, then the answer is "none".

If the design of the lathe allows the introduction of a transposition gear and optional change ratios, then the answer might be "a wide range of metric threads can be cut"

The transposition gear is a side-by-side pair of gears that does the inch/metric ratio of 25.4 mm/inch. For example, a 50 tooth gear connected to a 127 tooth gear. (25.4 * 5 = 127)

You can learn a LOT of interesting math by studying lathe's change gear schemes.

The Boston Gear Works and Martin Sprocket are two possible suppliers. I believe both sell through distributors. Make sure you know the Pressure Angle (PA) of the gears you wish to mesh with. Old lathes used 14.5 deg. PA. I believe 20 deg. PA is popular on newer lathes.

Good luck. Note that 16" lathe has a 10HP motor. That's enough ooomph to do some serious metal-peeling.

John Ruth

#### Mcandrew1894

##### Stainless
HI Southbend, Panza.....Southbend has got it right.

I just made a set of transposition gears for my lathe....Had to come up with a new thread chart too!....It was a very interesting exercise.
A gear tooth gauge will be helpful. My 1970's Logan has 16 DP and 14 1/2 PA.
If you can live with 0.0002" pitch error per inch of travel, you can use a 47/37 ( 1.2702) pair instead and avoid the usual problem of not being able to fit the gears under the gear cover. Most threads have more clearance than .0002"
and usually they are relatively short ( a couple of inches max usually)

If your making metric leadscrews for a machine tool or something where .0002" means something, forget it. Get the 127/50 or a 127/100.
Dave

#### Panza

##### Stainless

Excellent Mike ! That was what I thought they had. Is the slotted quadrant for adjusting the backlash/mesh when you change to a different gearset ?
Only need to find a high-speed-spindle version in good shape then
The other alternative is a Dean Smith and Grace. Seems far between the 2000rpm versions there too though..

#### rlbleeker

##### Cast Iron
I think the only difference in the 1000, 1500, 2000 RPM Pacemakers is the motor pulley and the speed chart. My 1952 20X96 came from Boeing and is set up for Metric.

#### johnoder

##### Diamond
Watch out for the "big" ones with 800, 1200 or 1600 top ends and eight drive belts.

John Oder

#### mulesandheelers

##### Aluminum
Watch out for the "big" ones with 800, 1200 or 1600 top ends and eight drive belts.

John Oder

Wonder what the max. HP these eight drive belts could pull or what was the biggest motor available in these?

Mine [20" x 72"] currently has a 30HP in it with the rear pulley being chipped and the #8 belt draped back over the motor.
The phase perfect is only rated for 20HP, in looking for a smaller motor will a 10, 15, or 20HP be best?

Then with the smaller motor shaft may have to get the another pulley made?

# 220280732434

#### johnoder

##### Diamond
The phase perfect is only rated for 20HP, in looking for a smaller motor will a 10, 15, or 20HP be best?

Then with the smaller motor shaft may have to get the another pulley made?

Depends on what is available. I had a new 7 1/2 I replaced a old 10 with on the 36" Ohio shaper. I just made a bush to adapt the bigger bore motor pulley to the smaller motor shaft. Actually this was more of an adapter than a bush since the motor pulley was a six groove job and quite long. The "bush" part of the adapter was shorter than this pulley and solid on the outer end, except where I drilled it for a cap screw to hold it on the motor shaft which I had tapped the end of. Had to make a key of course that went from keyway in motor pulley, thru wall of bush, and into motor shaft keyway, and naturally these two keyways were differing widths.

I'll bet a 20" "big" Pacemaker will do plently of good work with a 10 or 15HP motor and won't give the 20HP PP any heartburn. I think you said this was a 800 or 1200 top end job, Greg.
If it was mine and the chip did not seem to affect running balance, I would have no problem with running six or seven belts with the lower HP.

John Oder

#### Panza

##### Stainless
I think the only difference in the 1000, 1500, 2000 RPM Pacemakers is the motor pulley and the speed chart. My 1952 20X96 came from Boeing and is set up for Metric.

If that is the case then there is no point in paying premium for a high-speed model. Just change the motor pulley after you buy it

8 belts...

#### rlbleeker

##### Cast Iron
My 20x96 and 16x54 are both 15HP and my 14x30 is 10HP. I've got a 20HP PhasePerfect and they run great with it.

Here's a pic of the plate on my 20x96, hopefully you can read it. It cuts 1 1/2 to 92 TPI like the one in your link. Save you some math if you get a 40s or early 50s machine. The later, solid base machines, have a different thread range so this wouldn't be correct.

#### Attachments

• Pacemaker.JPG
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#### Mike C.

##### Diamond
The 25hp 20"er at work (one from the museum) has only four of eight belts on it. The guy I got it from said he was taking a 5/8" deep cut in 8" diam 4140 and it never hiccuped. I cannot imagine what it would take to stall this machine with four belts, let alone eight.

#### Panza

##### Stainless
Since I have the quick-change box off I thought I'd count the teeth on the gears to figure out how it all works once and for all.
I believe I have counted the teeth correctly but everything comes out 0,75X too low.The 1CE position should be 2 and so on. If I divide the input RPM to the main table by 0,75 everything is correct.

Gearing starts at the headstock with the 60 T. The gears on the same line are on the same shaft and rotate together. Red numbers is the tumbler options. Light blue are D/E lever, pink are A/B/C lever. Left column is RPM's. The main table uses 853,333 as the input and multiplies it with the ratios to the right and below (tumbler)and the TPI of the leadscrew.
Can't figure out what's wrong..

#### Attachments

• Gears.jpg
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#### E.F. Thumann

##### Cast Iron
A metric gear quadrant came with the 18" pacemaker I purchased a few months ago. I'm looking forward to your chart!

#### Panza

##### Stainless
Thank you John! It is obviously 4TPI, just went out and measured it now.
But that made my error even worse. The 1CE setting on the Quickchange should give 2TPI and not 0,75. There must be something amiss with with my gear calculations. I have figured it out another way but this is much more convenient, if it worked.

#### Attachments

• Gears2.jpg
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#### kitno455

##### Titanium
Working out alternate threading charts is one of my favorite puzzles. I've done a bunch of weird threads over the years, like module and DP worms, weird bottle cap adapters, optical parts, etc.

You don't need to know all the gears in the gearbox to figure this out. Effectively, you convert each pitch the box will cut into a ratio with the leadscrew pitch. So, all the gears in the box and the end gearing amount to 1:1 when you are cutting 4TPI, for instance.

Show us a pic of the end gearing.

allan

#### kitno455

##### Titanium
Actually, I think you need to switch the locations of the 120 and the 80 tooth gear on your lathe.

allan

#### Mike C.

##### Diamond
The magic input ratio to the QC box is 1.27:1. That makes 20 turns of the inch screw 25.4, which is the metric conversion. If you can figure a ratio that gets you close to this, you have your metric threading. 120/80 is 1.5:1. 120 and 96 would be closer at 1.25:1. You may also need more change gears to do other metric threads. The Enco at teh hydraulic shop had three change gear charts for metric threads. 95% of the more common pitches could be cut in the simplest position (that also converted directly to inch threading). I never had to change it for .5, 1, 1.25, 1.5, 1.75, 2, 2.5, 3mm, etc... but the other two setups covered all the metric threads.

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