Dividing

[BoldminerParticipant @boldminer]

I wish to index for 198 teeth using a BSO dividing head with a 40:1 worm-wheel. The problem is that the supplied dividing tables give the same results for both 198 and 197 ie. a 20 hole plate at 4/20. This cannot be correct for both, can anyone help please ( 198 ). Do I need to make a special plate ?

[BoldminerParticipant @boldminer]

[Brian WoodParticipant @brianwood45127]

Hello Boldminer,

The ratio N=4/20 appears repeatedly for several divisions but they are differed by the gearing used on the studs to give the indexing required.

In your case, T=197 divisions has the gears as H=20, A=24,B=40, Cand D have no values and E=48

               For T=198 divisions those gears are H=20, A=24, B=40, C=32, D=48, E has no value

Don't forget you are using the compound indexing method to achieve what you want, where movements are both forward and backward as dictated by the gearing to arrive at the result.

My tables for the BSO device go all the way out to T=380.

I hope that helps you

Brian

 

Edited By Brian Wood on 25/01/2013 16:14:25

[Les Jones 1Participant @lesjones1]

Hi Boldminder,
I do not believe you can divide by 198 using a 20 hole plate. Each move needs to be 360/198 = 1.818181818 Deg. As the gear ratio is 40:1 then one revolution of the handle (An division plate) will be 360/40 = 9.0 Deg. As the plate you want to use has 20 holes this give 9/20 = 0.45 Deg per hole. 1.818181818/0.45 does not give an integer result so that plate can not be used. I think you will need a plate with 99 (Or 198) holes in it. With a 99 hole plate you would move 20 holes each time. (40 for a 198 hole plate.) You could make the plate using the dials on the handle. You would need to move 360/99 = 3.6363636 degrees for each hole. (3 Deg, 38 min, 10.91 Sec) You would need to work out all 99 settings before hand and round each value to the smallest reading on the dials.

Les.

[JasonBModerator @jasonb]

The 20 hole plate will work because the compound indexing means you are not really using a 40:1 ration.

Have a look at this PDF of the possibilities which is what Brain is suggesting.

**LINK**

[JasonBModerator @jasonb]

Further to the above it sounds as if you are looking at the plate and ratios for a BS2 universal head when you only have the semi-universal BS0 head in which case its make another plate, 22hole would be the least work and index each hole. 22 can be done from teh plates you have or if you have a DRO then the PCD function will aqlso set them out

From the charts in my link above a BS0 head will only do the numbers on the chart where H & N are shown and the rest are blank

 

Edited By JasonB on 25/01/2013 18:46:54

[BazyleParticipant @bazyle]

Your 4 holes on 20 plate gives 200 teeth …..hey near enough

Factors of 198 are 2,3,3,11 so you would need a plate with a multiple of 11 for a start for plain indexing. You probably have a 33 hole plate which would give you every third hole spot on.
Before you dismiss that, depending on your application, you may be able to fill in with adequate accuracy. You need to step 13.33 holes. If you work out what that is as the cord of a circle you can make a small strip of metal with a pin to go in the hole you have just used and a hole at that distance. As you should be able to drill using your mill to an accuracy of a few thou the error will be minimal for everything short of a telescope tracker.

BTW I'm not sure a 22 hole plate indexing every hole is right.

Edited By Bazyle on 25/01/2013 19:27:48

[BazyleParticipant @bazyle]

No, I;m a bit off.

33 gives you every 6th hole so it is a bit more involved. Make a strip to get you half way first.

[JasonBModerator @jasonb]

Posted by Bazyle on 25/01/2013 19:21:12:

BTW I'm not sure a 22 hole plate indexing every hole is right.

No its not is it that would give 880divs, what a div.

[Brian WoodParticipant @brianwood45127]

I've made additional plates for my BSO head which give prime numbers up to 69, it does extend the range quite well for simple indexing. The plate size limiit was reached when any larger would mean mounting the head up on spacing blocks to be able to turn the handle without being forced to have it overhanging the bed on the mill. I was lucky too that my tables came with the BS2 factors shown and these of course show the doublets applicable to the BSO head that can be selected from the standard plates.

What of course we are all overlooking is all the other odd numbers up to 198 and the means to achieve them.

I am tempted to suggest to Boldminer that he questions the number of teeth to cut and thinks of other DP gear sizes that he can index for around the periphery. 198 would be a lot of teeth to cut and are they perhaps too fine a pitch for the application?

Brian

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

198:40 will give 0 turns and 4 hole in indexing plate #1 with 17 hole.

 

Edited By Jens Eirik Skogstad on 26/01/2013 10:04:55

[John Stevenson 1Participant @johnstevenson1]

Graham has it correct.

It's 40/198 not 198/ 40 which would be 4 turns plus a few holes.

As Bazyle says the factors are 2,3,3,11 and of these figures only 2 will go into 40 giving what Gray says, 20/99

 

Using division plates is one area where decimal doesn't work and you have to keep to fractions.

Edited By John Stevenson on 26/01/2013 13:13:54

[BoldminerParticipant @boldminer]

Thank you very much to everyone that took the trouble to reply to my ' division ' query. After reading through all the replies it became obvious to me that what I have is a simple BSO dividing head with no possibility of compounding. So the information in the 'tables' is correct when you can compound using the rest of the infomation for the particular application. The clock I am making is a 'Large Wheel' skeleton clock by John Wilding but again what I overlooked was the fact that he was using a Myford dividing head with a 60:1 ratio.

After following Mr Jones's example using a 99 hole plate I have calculated that the equation results in an error of only .000011 per division which as I used to say is "good enough for the pit". So, now all that remains to be done is to visit a local engineering co. for material for a new plate.

So once again thank you Les and the rest of you gentlemen for you time and trouble.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Posted by Jens Eirik Skogstad on 26/01/2013 09:43:18:

198:40 will give 0 turns and 4 hole in indexing plate #1 with 17 hole.

Edited By Jens Eirik Skogstad on 26/01/2013 10:04:55

Sorry, it is my fault.. it will be 20/99..

[John Stevenson 1Participant @johnstevenson1]

Posted by Boldminer on 26/01/2013 13:21:08:

After following Mr Jones's example using a 99 hole plate I have calculated that the equation results in an error of only .000011 per division which as I used to say is "good enough for the pit". So, now all that remains to be done is to visit a local engineering co. for material for a new plate.

Sorry do not understand this?

20 holes on a 99 circle plate will be bang on – no error ?

[Les Jones 1Participant @lesjones1]

Hi Boldminer,
As John says there will be no error using a 99 hole plate. The reason you think there is an error is because I used decimals in my explanation. 360/198 does not have an exact decimal equivalent even if you went to one thousand decimal places. As John says in his post at 13:12 "Using division plates is one area where decimal doesn't work and you have to keep to fractions."

Les.

[NilochParticipant @niloch]

Hello Boldminer,

It may sound trite, smart alecky and unhelpful for your circumstances but the sale of my Myford dividing head in its original packaging plus one of Mrs Stevenson's plates raised 85% of the purchase price for one of these

I have used it to cut three of the large wheels for Wildings clock. A big thank you to Mr Jeffree – the designer!

Edited By Niloch on 26/01/2013 16:57:44

[BazyleParticipant @bazyle]

However the person who bought the myford head will be able to pass it on to his great grandson in perfect working order, whereas you electronic gizmo will be landfill before you are.

If I read it right Boldminer is aiming to make a 99 hole plate now. The way to do that of course is to use a 198 hole plate and step 80 holes.

[John Stevenson 1Participant @johnstevenson1]

Posted by Bazyle on 26/01/2013 17:45:36:

However the person who bought the myford head will be able to pass it on to his great grandson in perfect working order, whereas you electronic gizmo will be landfill before you are.

If I read it right Boldminer is aiming to make a 99 hole plate now. The way to do that of course is to use a 198 hole plate and step 80 holes.

.

??????????????

If he had a 198 hole plate he wouldn't need a 99, he'd just go 40 holes on the 198 instead of 20 on the 99.

What you say about the Myford dividing head is true, it will be there in a 100 years.

However depending on what you use them for the electronic ones can have paid for them selves in a fraction of the time.

I have a division master and must admit I'd be dead in the water without it. One job I get regularly are odd number straight sided splines. usually a prim number like 13.

So setup with the cutter half a spline width over, cut the side, index round 13 times, move cutter over half a spline tother way, index round 13 times.

Go back to central, index round 1/26th to get the gap central then swap back to 13 divisions to clean the root up.

Job done and it doesn't matter if the phone rings whilst you are doing it.

[Author]

Posts