Cutting BA and imperial threads on a Cowells

[steamer]

Hi Jo,

The 37/47 gear set and it works very well... You could do far worse.

Dave

[Dan Rowe]

Dave,
Yes it was your tip and every small US thread I have checked has a small error solution that and the fact that both gears can be cut with a #3 cutter makes it a really sweet combination.

 
Dan

[swilliams]

This all looks pretty cool. Fitting all the wheels on such a small lathe must make things a little more difficult. Impressive how fast the plans all come together.

I want to see some snaps of you cutting a 16BA thread, preferably internal 

Steve

[steamer]

Ive cut 128.  Depth of thread is about. 004"
DONT DISENGAGE THE HALF NUT!
Dave

[Jo]

Ive cut 128.  Depth of thread is about. 004"
DONT DISENGAGE THE HALF NUT!
Dave

Cowells don't have half nuts, only completely nutty operators.   

Jo

[steamer]

Well Jo....I can say their nutty.....Not enough data...but I'd shoot for pleasently Zanny!

 

[Dan Rowe]

Jo,
Not all the combinations that you posted from NthreadsP are workable solutions. Here is the graphic that I redrew that is on the UK lathe site so other folks have a shot of following this.



You entered the 2 compound gear from the power feed or auto-traverse set which is what I did also. The program gives 4 gears 2 are drivers the other two are driven. The first and last gear are the spindle and the lead screw. The middle pair is the compound gear. The compound gears in the set are 20/56 and 16/32.

So the only 56 and 16 gear are compound gears so they have to be in the middle pair with the matching gear for a solution with a standard gear set. We also have to be on the look out for double 20 and double 32 gears as it is counting one of the compound gears.

I have a nifty gear drawing program so I will draw the whole set and the quadrant to see if the solutions are workable with the existing gear quadrant. My backup plan is to use the original quadrant for the power feed only and design a new quadrant to get both left and right hand versions of the threads used by a model engineer.

Dan

[Jo]

I have a nifty gear drawing program so I will draw the whole set and the quadrant to see if the solutions are workable with the existing gear quadrant. My backup plan is to use the original quadrant for the power feed only and design a new quadrant to get both left and right hand versions of the threads used by a model engineer.

Dan

I love a volunteer. I won't rush to cut anything.

Jo

[Dan Rowe]

Jo,
I finished drawing the parts and I thought about left hand and right hand threads. The chart in the Cowells book shows 2 idle gears and states for left hand threads only a single idle gear is used.

The compound gear drawing shows the same number of reversals as the book drawing so it will be a right hand thread with a compound gear and a single idle gear. The left hand setup does not use an idle gear only the compound gear is needed. If that passes the two  logic test the plan is looking good.

 
Dan

[Jo]

Dan,

When you draw this out don't forget that we can do an idler which is a double width gear that engages both the linner and outer gear chains. The smallest this could be is a 16 tooth gear.

Jo

[Dan Rowe]

Jo,
I had not thought of a double thick gear but I think we can get very close with only cutting a 37/47 set of gears and making a single keyed bushing.

I took the compound set of gears out of the standard set I was using in NthreadsP. To keep the error small I used the 16/32 gear in four of the solutions. The 16/32 gear will change the effective pitch of the lead screw to 0.5 or 2.   I just used the standard set and changed the pitch of the screw to 0.5 for the solutions. I did not find any use for the 20/56 gear.

Adding the 16/32 will work fine for the right hand threads but the left hand combination will need an idle gear which might be a problem.

To make sure we are on the same page the gear set I am using is the standard set with the auto-traverse gears and the screw cutting kit, 20,25,30,30,32,35,40,50,64,37 & 47 and 16/32 and 20/56 compound gears.

I will check the combinations graphically and if there is a problem I can go back to NthreadsP for alternative combinations.


0BA     Driven gears  30  Driver gears  30   Pitch 1    error %  0 (Simple)
1BA     Driven gears  40  25  Driver gears  30  30   Pitch 0.9    error %  0
2BA     Driven gears  20  Driver gears  25   Pitch 0.8    error %  0 (Simple)
3BA     Driven gears  47  35  Driver gears  30  40   Pitch 0.729    error %  0.070
4BA     Driven gears  35  40  Driver gears  25  37   Pitch 0.660    error %  0.108
5BA     Driven gears  47  40  Driver gears  30  37   Pitch 0.590    error %  0.072
6BA     Driven gears  35  40  Driver gears  20  37   Pitch 0.528    error %  0.270
7BA     Driven gears  40  47  Driver gears  30  30   Pitch 0.478    error %  0.266
8BA     Driven gears  64  47  Driver gears  35  37   Pitch 0.430    error %  0.120
9BA     Driven gear  64   Driver gear  25   Pitch 0.390    error %  0.159  (Simple)
10BA   Driven gears  40  50  Driver gears  20  35   Pitch 0.35    error %  0
11BA   Driven gears  30  47  Driver gears  25  35   Pitch 0.310    error %  0.091 (use 16/32 also)
12BA   Driven gears  40  50  Driver gears  32  35   Pitch 0.28    error %  0 (use 16/32 also)
13BA   Driven gears  40  50  Driver gears  20  25   Pitch 0.25    error %  0
14BA   Driven gears  37  47  Driver gears  25  32   Pitch 0.230   error %  0.007 (use 16/32 also)
15BA   Driven gears  64  37  Driver gears  20  25   Pitch 0.211    error %  0.544
16BA   Driven gears  64  37  Driver gears  30  30   Pitch 0.190    error %  0.017 (use 16/32 also)


26TPI   Driven gears  32  40  Driver gears  25  50    TPI   26.00    error %  0.036
32TPI   Driven gears  40  37  Driver gears  25  47    TPI   31.99    error %  0.021
40TPI   Driven gears  40  37  Driver gears  20  47    TPI   39.99    error %  0.021
60TPI   Driven gears  35  50  Driver gears  20  37    TPI   60.06    error %  0.112


 
Dan

[steamer]

As a matter of reference, I needed to cut a double wide stud gear to use the transposition set on my lathe

Dave

[Jo]

I have just checked my dividing head. I don't have the plates for my dividing head to do either the 37 or the 47 . I can do 27, 33, 39, 45 and 52 easily.

To do the 37 and 47 I would need to knock up another plate. It is easy enough using the DRO but it will cause delays as i will need to get a piece of 4 1/2" dia * 3/16" plate to make it out of .

Jo

[steamer]

Jo

Is it the standard size B&S 0 index plates?

I have a couple extra I believe....I'll check the hole counts.....though shipping costs may exceed the price of the raw stock!

Dave

[Jo]

Is it the standard size B&S 0 index plates?

I have no idea what the standard size is.... but thanks

I have just found a old 5" cast iron pulley that is asking to be converted into something useful So I have the sacrificial material for the plate.  The DRO did not complain in the slightest when I asked it for a 47 hole circle so it is looking possible. Just need to know from Dan if the spacing is a go'er.

Jo