53 tooth gear

So this is the first time i have ever needed to cut a gear and its a 53 tooth one, i have a rotary table with dividing plates but no 53 plate. So i was thinking i have a mill with a dro that can do pcd's, so i could use this to make a 53 plate. Now here's my question my rt is 90/1 so after alot of reading i think i need 1turn and 37 holes ? does this sound right ? I have no engineering training at all apart from books ie workshop practice series. thanks

Mark,

I agree. The rationale is as follows. To make one full turn of the rotary table takes 90 turns of the handle. To divide a single turn of the table into 53 equal parts we need to turn the handle by 90/53 each time. Since 53 is a prime number we cannot simplify the improper fraction. However we can express it as 1 and 37/53. If we have a 53 hole plate then it is simple! Here's a picture of a 63 and 69 hole plate I made for my dividing head, to cut 63 and 69 tooth gears, because I was too idle to set up the gears for differential indexing:

Remember that any errors in the dividing plate will be divided by 90, which is good.

Regards,

Andrew

Thanks Andrew, I'll give it a whirl and see what comes out .We never did any fractiions/prime numbers etc at school, takes abit of getting yer head around.

Edited By mark mc on 14/11/2012 09:42:00

Hello Mark,

Your calculations are correct, 53 hole plate, 1 full turn and 37 holes, will give you 53 divisions on a 90-1 rotary table.

Here is a picture of a 95 tooth 6DP gear I cut last week, on a rotary table.

Richard.

Edited By RICHARD GREEN 2 on 14/11/2012 09:44:28

Good lord Richard that's scary looking to me, but looks very nice too. thanks for replying. Off now to make a 53 hole plate, hopefully....

Sorry to sound thick but if you need to make 53 tooth gear and can cut 53 hole plate well whats the problem?.

but if you mean 37 hole plate ok but how is that easier?

sorry but not completely familiar with RT and dividing heads

90/53 ok get that

90/53 = 1 + 37/53 -- ok here too

how does a 37 hole plate help..?

You don't use a 37 hole plate its one full revolution and 37 holes of the 53 hole plate

1 rev =53 plus the 37 equals 90

So 90/53 gives the fraction needed

Another way to look at it.

360 divided by 53 means each tooth is 6.792degrees.

with a 90:1 ratio on the table, one turn gives 4 degrees add that to

37/53 of a turn (0.698x4) = 2.772 and that gives you the desired 6.792deg rotation

I don't think mark has a problem just wanted his calculations confirmed

J

Edited By JasonB on 14/11/2012 15:16:10

If you only want one gear it is hardly worth making a dividing plate. As Jason has pointed out the angular rotation between teeth is 6.792 degrees = 6 degrees 47 minutes 31 seconds. Just make a table of the angular rotation required for each tooth ie 6.792, 13.584, 20.376.......etc until you hav done a complete revolution. Convert this table into degrees, minutes and seconds. Then just increment the rotary table to the required angle for each tooth. It requires a little concentration but is perfectly doable.

Mike

Ahh JasonB (this might get confusing).. so he can "do 53" with the dro ......

thus 90/53 = 1 +37 holes of 53 plate......but if you have 53 plate why not index one hole per tooth?

Michael .. coming to this from CNC land thats how I would have done it ( with a suspecious eye on rounding errors..).... ....

Ahh well , it is to learn that we live.

You can't do that with a rotary table as you need to take into account the 90:1 reduction, going one hole at a time would give a 4770tooth gear.

If you were using teh plate for direct indexing on say the lathe spindle then it would work

I agree, don't get too hung up on exact dividing.

My home made rotary table is geared 60:1 and has 60 graduations on the dial.

I use excel to produce a table of the readings and work around a gear using that.

The maximum error is half a division or 0.05 of a degree. For a 2" diameter blank that's 0.00087" or less than a thou.

When I had to read maps or use burettes I had to estimate tenths of a division. If you can do that the error approaches a tenth of a thou or about five wavelengths of red light...

In other words a division plate is NOT required to work within industrial tolerances for typical model engineering gears.

Neil

Edited By Stub Mandrel on 14/11/2012 20:07:59

The OP says that his rotary table has provision for dividing plates, so why not use them? Also, we do not know the diameter of the gear to be cut; the bigger it is the more accurate the division need to be.

I will be cutting my traction engine final drive gears on a rotary table, as per Richard's setup, as at 14.8" diameter they will not quite fit under the milling machine arbor. I am budgeting for an error of 2 thou at that diameter and will compensate for it by cutting the teeth slightly deeper. That's accuracy of course, not resolution, which is quite a different thing.

Regards,

Andrew

The gear is for a small worm drive inside a single drive unit for a wheel chair, it's only around 62mm dia and some bright spark thought it would be great idea to make it from plastic with teeth that have no profile at all, the look as if they have been cut with a hack saw, dead straight no kidding. Didn't get much time in the cave today but I'll get the plate finished tomorrow, again thanks all for the help.

.... oh, I don't think so. 5 x 700 nm ?

More like green light? - Andrew

You can make an approximate plate for reuse to make a better one using any existing plate, or a change wheel by the multi-turn method.

Say you have adapted a 60 tooth change wheel to fit the rt which gives 60 x 90 = 5400 steps all round the circle.. You want 53 so you need to count 5400/53 steps = 101.887 steps. But you can't step a fraction. So miss the first tooth (or hole) and see if you can do the second ie 2 * 101.887 = 203.774.

Still no good but keep going and you get to No 9 = 916.981. Ok so do 917 steps and you have only a slight error. Repeat the process and you eventually fill in all the teeth with a bit of an error by going round multiple times. the error is spread all over the target not built up progressively. But when you use that as the index device the error gets reduced.

This is what the stepper motor dividing gizmos do. Some combinations work better than others but basicly any existing plate can make any new plate.

380 to 760 nm (400-790 TeraHertz) is generaly accepted as visable light

so for rock and roll 500nm or 0.5 um (microns) will do.

anyway OP seems sorted and I will work on my problem of gettinng comfortable with division as required in the future {if required}..though I am sure to find a application {not an app} somewhere

Thanks anyway.

You're right. I had about 450nm in mind as a typical 'wavelength of light', so perhaps I should not have guessed the colour.

Even so, it always surprises me that the difference between the small you can relate to (i.e. working toa a thou or less) and the small you can't quite grasp (wavelength of light, size of animal cells or even bacteria) is not really very much at all.

Neil

Just been thinking about this and still cannot see why greater division accuracy would be needed if the gear is larger.

Angles are angles, but if this gear is 'large' then the one it meshes with will be larger by the same proportion so the angular error will be the same.

If there are errors of spacing beween the teeth causing varying backlash or binding this would actually be more problematic on very high DP gears like in a watch, than it would on ultra large gears on say a traction engine.

Ian

From my old Machinery's Handbook tooth-tooth tolerance barely increase as gears get bigger, but gets bigger more or less in proportion to tooth size.

It will upset the clockmakers, but the recommended gear quality for clocks is in the lowest category with milking machines and kitchen blenders, below hair and hedge clippers, with gun data computers and gyroscopes at the top.

Neil