# a few questions on the 3996



## anectine (Dec 16, 2012)

Hello everyone, like to wish everyone a merry Christmas!  I know it's a little early but I have a full schedule for the next 2 weeks and didn't want to forget the well wishes.

Ok since 1st post here on my "new to me" 3996 I have fixed the QCGB and it is running!:thumbsup:  The only thing is it runs FAST!:thinking:
I suspect the previous owner has made some mods to the drive system.  Here is what I found

1/2 hp 115v 1725 rpm reversable motor with a 3 step pully 4.5"- 2.5"
Lower shaft has a 4 step pully 4.5"-1.5" inside and a 4 step on the outside 5.5"-2.5"
the outside upper shaft has the same step pully %.5"-2.5"

Here are my questions


Is this correct?
Is 1/2 hp enough (i put the lathe in back gears, tensioning lever all the way up, spindle still turned and motor smoked the shop up no time flat)
I have a 1.5hp 1725 rpm 115/220 11 amp motor I used on a wood lathe for a very short time.  Would this be over kill?
I have searched the manuals that came with my machine but cannot find the correct pully diameters.  Anyone want to measure theirs for me?

Oh yeah anyone still use the old rocker tool post?  I am thinking of buying an Aloris knock off.  What is the difference in piston and wedge designs?

I know this is a lot to ask, I'm new at this and loving the smell of old grease!  I'm not too sure my wife is though


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## pdentrem (Dec 16, 2012)

Ask away.

I would suggest that you get a manual for it. There is a online version on the Atlas/Craftsman user group in yahoo groups. Also you can get a reprint here.

http://www.ozarkwoodworker.com/ATLA...-Metal-Lathe-3995-3996-Parts-Manual_p_47.html

The motor has a 2 step pulley that in turn spins a larger 2 step on a jack shaft. The other end of that shaft has a 4 step that drives another 4 step on another jack shaft. That second shaft has a double pulley that drives the spindle via 2 matched belts. Between the 2 step and the 4 step you can get 8 different rpm settings plus 8 more using the back gears.

Likely the bull gear was not released from the spindle when you tried it is back gear?

1/2 hp or 3/4 hp is enough.

I moved over to a Phase II clone wedge style from the piston style. AXA is the proper size for these lathes. Some have used BXA versions which are taller and bigger, but required as the lathe is not really stiff enough to use the larger tools to the fullest.
Pierre


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## wa5cab (Dec 18, 2012)

anectine,

Starting at the spindle, the 2-groove pulley on the inside end of the upper counter shaft (jack shaft) should be the same diameter as the 2-groove pulley on the spindle.

The two 4-step pulleys on the outside ends of the upper and lower counter shafts should have an OD of 6/5/4/3.  The little end of the upper pulley should be inboard (nearest to the wall of the cabinet).  The little end of the lower 4-step should of course be outboard.  They will work if both are turned around but the results won't match the chart.

The right end of the lower countershaft (inside the cabinet) should have a 2-step pulley with OD's of 9.0" and 7.5".  The smaller diameter should be to the right (nearest the end of the shaft).

The motor pulley should be a 2-step with diameters of 1.930 AND 4.390.  Odd dimensions but I and a Yahoo Atlas_Craftsman group member who did a drawing and made one both got the same figures off of an original pulley.  The largest diameter is nearest the motor.

All diameters are outside diameters, not pitch diameters.

I have a 3/4 HP single phase 240 V motor on my 3996.  As Pierre said, you don't need anything larger.

If you don't know where the back-gear lock pin is, it is on the right side of the bull gear.  It locks the bull gear to the spindle pulley when not in back gear.  To find it, open the headstock top cover and rotate the spindle.  It just pulls straight out.  If stuck, it has a narrow groove on the right end that you can hook into to get some pulling force on it.  It isn't unusual for one that hasn't been moved in years to be stuck.

I'll comment on tooling later.

Robert D


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## anectine (Dec 18, 2012)

Thanks you guys this is a big help!  
The odd thing about the motor smoking was that I did have the bull gear pin out.  I made sure I read the instructions before I tried this.  I will have to see if I can trade the 1.5 for a good 3/4.  I think I will put the 1/2 hp  on my under powered wood band saw  it is being run off of an old washing machine motor that is at least 40 years old.  I think it is time for an upgrade there.

Thanks again

Adam


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## wa5cab (Dec 19, 2012)

OK.  Disengage back gears.  Open headstock top cover.  Reach down with a finger to the large back gear and see whether it turns freely.  Lubricating the back gear bushings on the commercial models isn't easy and tends to get forgotten.

On tooling, I have a Yuasa 100 series set.  Same size as the AXA.  It has given good service for 30+ years.  I have the complete lantern tool post and all the holders still in the fitted steel case.  It's still in NOS condition.  I keep it only for nostalgia reasons.

On wedge versus piston type QCTP, generally the wedge type is more expensive.  I suspect this is the reason some people assume that the wedge type must be superior.  I am inclined to disagree for the follow reasons.  Both types have a solid dovetail on the tool post and the same holders fit both.  The difference is in how the holder is pushed out against the dovetail on the post.  Considering tolerance buildup in the wedge type that is not a consideration in the piston type, I can see a theoretical reason why the wedge type could have poorer repeatability, not better.  Never mind that the selling specs say otherwise.  On the other hand, the wedge types as sold do have slightly greater surface contact area in the locking position than the equivalent piston type from the same contractor.  But I wouldn't trade my 30 year old piston type for a new wedge type.

On carbide versus hand ground High Speed Steel cutters, I also disagree with the folk lore.  For 30+ years, I haven't used anything but carbide.  Grinding cutters takes time.  The older I get, the less time I have.  I sometimes use brazed carbide cutters.  And have a lot of them.  But mostly, I use a combination facing and turning holder that takes replacable inserts.  For parting off, I mostly use Thinbit holders with an assortment of replacable carbide blades.  They are also useful for cutting circlip and O-ring grooves.

YMMV.

Robert D.


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