Dro units

Hi all this is my first post. I have had a boxford bud lathe for a while and have had great fun making tooling for it and have just bought an a Amadeal milling machine with a dro pros dro fitted. I was hoping to make a 127 hole dividing plate to make a conversion gear for the boxford but after playing with it for a while it seems I can only go up to 99 holes on the pcd function. Am I doing anything wrong and has anybody had any experience with these units. Many thanks in advance Cliff

Hello Cliff,

Even the Newall PCD function only goes up to 99 divisions so you are not making any mistakes.

Rather than grapple with making an awkward 127 hole change wheel, you can use a combination of 63/80 instead. The error difference is too small to worry about and Southbend themselves recommended the combination as a good working alternative.

Regards Brian

I dont know much about dro`s but cant you use the bolt hole circle function,they go up to 360 dont they or am i talking gibberish. I thought i read this the other day for an anilam wizard.

I think that Anilam is a CNC controller, not a DRO!

How large a plate do you want, and what size holes? I think I have a spare aluminium circle somewhere, it would be a matter of moments to sling it on the CNC mill and drill a plate for you if you only want something that'll be used a few times.

Just tried 127 on my Sino readout and it accepted it with no problem. I used a pcd of 360mm. what pcd did you use, as that may be the limiting factor (if you post the pcd you used I'll try that in my setup)?

The maximum number of holes you can enter in the PCD function of the Newall DP700 readout (fitted on my Myford S7) is 999

Also the Anilam Wizard and Mini-Wizards I've used in the past are DRO's

Nick.

Edited By Nick Hughes on 13/11/2017 12:05:17

If your unit won't go over 100 then do 64 holes over an angle of 178.68deg and then a second set of 64 over 181.42 using same center location and PCD

For the degree of error involved [1 part in 10,000] between 100/127 and 63/80 it really isn't worth the trouble of making a change wheel of 127 teeth.

Clearly my Newall PCD function has been updated by more recent models. Cliff will decide which way he wants to go in the end---I was only pointing out that a wheel of that size is maybe redundant for the average metric gear cutting that most hobby engineers undertake.

Regards Brian

On my south bend 9 a , i just make the change gear out of tufnol as and when required to cut metric threads with the least possible error. Last one i cut was for a 2mm thread. I bought a boxford 79 teeth and made i think a 20 or 24teeth one from tufnol.

You can do a lot of metric threads with a 79 teeth gear + one of either 20,24.30 and 40 teeth .Though i have the gear box on my south bend.

Hi thanks for all your replies, My lathe is metric so I would also need a 135 tooth gear to make a compound( should have made that clear I guess) but was just unsure if I could do that many holes on the dro. Is there another combination i could use other than 135/127. The next time I get up to the workshop I will try increasing the pcd to see if it allows me to do more holes as I only selected 200mm. Again thanks for all of your input I look forward to your responses.

You just fit the 100/127t gears back to front. Nobody has a 135t gear, AFAIK.

Murray

Or 63/80t may be more convenient.

Edited By Muzzer on 13/11/2017 21:56:03

Hello Cliff,

The alternative for a 135/127 combination is 50/47, used on the lathe with the 47 tooth wheel as the onward driver. I'm sorry to say Murray is incorrect, you can't just reverse the other combination because the leadscrew pitch has also changed to 3 mm from 8 tpi

Regards Brian

In that case you'll need to write to all the major manufacturers and get them to correct their manuals!

The maths is very simple.

If you have a 3mm leadscrew (like the example in hand), and you want to cut imperial, you need to speed up the leadscrew slightly. The simplest example would be to cut an 8tpi thread which has a 25.4 / 8 mm pitch ie 3.175mm. So for that you drive the 120t gear and the 127t gear drives the 3mm leadscrew gear. This gives you the correct ratio, as 127 / 120 x 3 = 3.175.

Going the other way, if you have an 8tpi leadscrew (3.175mm again) and require a 3mm thread, you need to slow down the leadscrew by that ratio. So you drive the 127t and the 120t will drive the leadscrew gear.

It's really not rocket science.

Murray

Tom Lipton has a neat solution to this problem on his Blog where he made a 127 hole plate for his spindexer using a method similar to that described by JasonB but used 3 different PCDs and the same angle for all holes:

Hello again Cliff,

A further variation which might be more useful is 80/85, with 80T as the onward driver

The maths are; 127/135 = 0.94074 and 80/85 = 0.94198

You might even have these wheels as standard supply

Regards Brian

Hello Murray

Now you are talking about a combination of 120/135 which is very different. I agree with that. No need now for a letter to the manufacturers!

Brian

Brian

Cliff,

A small error in my suggested 80/85 combination. as a substitute for 127/135

The decimal value is better than I stated earlier at 0.94118 which is only 0.00044 larger than the 127/135 combination value of 0.94074. The working error will be small..

Murray

My apologies, I misquoted your combination as 120/135, it should of course have been 120/127, it has been nagging at me this afternoon

Regards Brian

Edited By Brian Wood on 14/11/2017 18:04:01

Thanks for your replies. Brian I already have a spare 80 tooth gear so would only need to make an 85 tooth gear so I think this is the best way forward for me, many thanks.