Pitch Circle on DRO problem

[Martin King 2Participant @martinking2]

Hi All;

Got some spare time so thought I would do a bit on my 10V. Thought I would try a pitch circle of 5 holes for the cylinder covers, so watched some YouTube vids and looked pretty simple.

Entered 0, 0 for x &y axes after centering up the part with an edge finder,

To be on the safe side I am using a sharpie in the chuck not a drill bit, very glad I did!

Went into the circle function, set the centre at 0,0; diameter 1.125"; no of holes 5; start angle 000, (3 O'clock); end angle 360 and off we go..

NOT!

I only get 4 holes with the 5th back in the starting place! What gives please?

DRO is a SINO unit

Cheers, Martin

[Martin King 2Participant @martinking2]

[JasonBModerator @jasonb]

Either add 1 to the number of holes or set the ending angle to one space less eg 288 (360-72)

[Martin King 2Participant @martinking2]

Hi Jason, Thanks! So if I wanted 6 holes I would set 7 or back off the angle by 30 deg? Seems a bit odd and does not happen in the YT videos? Perhaps a SINO DRO quirk?

Martin

[JasonBModerator @jasonb]

60 deg if a 6 hole PCD, finish at 300 or start at 30 and finish at 330 depending on how you want to lay out the set of 6

[Martin KyteParticipant @martinkyte99762]

It's doing exactly what it says on the tin. You asked for five holes with the last hole at 0 (or 360 deg). When designing the interface for the DRO the requirement is for a general way of spacing a set number of holes around a circular arc.

If you cannot be bothered to calculate the end angle for a full circle of holes you specify an extra one and don't drill the last one because it's already where you put the first one.

regards Martin

[Anonymous]

More than a bit odd, positively bizarre! On my DRO (Newall) a PCD is enter centre co-ords, enter diameter, enter number of holes and start angle. The next button push gives the location of the first hole and so on. It'd be a right royal PITA if you had to take into account the actual start and/or finish angles. If I want a large hole I often get rid of the waste by drilling a series of slighly overlapping holes just inside the final diameter. They are usually odd numbers in the range 30 to 40. So start/finish angles would be non-integer numbers.

Andrew

[NealebParticipant @nealeb]

My Easson also asks for start/end angles. Makes sense as it allows for holes around part of a circle. It's a question of flexibility against ease of use, I guess, even though most of the time you are going to use the "whole circle" method.

I've always worked out the end angle (using the calculator on the DRO if needed!) but I hadn't thought of adding one to the number of holes and using 0 as start and finish. Clever wheeze!

[JasonBModerator @jasonb]

Yes it does seem a bit odd but once you have found out what the DRO needs entering the first time you do a PCD it becomes second nature after that.

As for odd angles when stitch drilling circles I just divide 360 by the number of holes and subtract the answer from 360 to get my ending angle or more often than not see what fits in Alibre and adjust the PCD slightly to suit a common drill size such as 6.0mm and can easily get the angle from that, easy to enter angle to 3 decimal places. Seems to work OK as all that is needed is a tap with a hammer and out drops the waste.

Then you can do it all over again!

[NealebParticipant @nealeb]

One of the optical scales that came fitted to my Smart and Brown has recently failed, and having now become used to a DRO on a lathe, I've been researching options for replacing/updating. As a result, I've actually read a DRO manual a bit more carefully!

I have also used the PCD technique for drill-and-break-out hole-making, but it seems that there is also the option to use the arc ("R" option on the Easson) which automatically sorts out hole overlap, tool diameter, etc, although you might need to do the job using several arcs as I don't think it will quite manage a full circle. Something I'll try out next time I need to do this.

On the other hand, I hadn't thought about using CAD to lay out the hole pattern for this; I've been doing sums while standing at the machine which is a little bit fraught. More than one way to skin the cat…

[Martin King 2Participant @martinking2]

Hi All,

Thanks for the advice, all went well with both covers now done and cylinder drilled and tapped.

Found that I had not quite machined enough from the underside flange of the standard so the 7BA nuts do not quite sit down flat. Will put it back on the lathe and take off a gnats or two!

Looking forward to doing a bit more now that I have got my enthusiasm back!

Cheers, Martin

[Martin Johnson 1Participant @martinjohnson1]

Martin,

If you have one of the Chinese DRO units, (mine is badged Sinpo) then hole PCD's are "interesting" and the Chinglish instructions are not a lot of help either. My experience is largely as you describe. I find the hole centre has to be 0,0, but I can see no reason why this has to be. Most times I can get it all to work, but sometimes it just seems to throw a fit and direct me to very strange places on the work – cannot work out why yet.

The moral of all this, run round the PCD with a pointer before you drill (or just mark the surface with a centre drill). Fortunately as with all things digital it is either right or very wrong, so easy to tell.

Martin

[JasonBModerator @jasonb]

Should not be a problem getting the PCD to put the ring of holes around any given points, I have done several sets of holes on a single plate of metal.

If you can't get that to work then use the absolute to position the spindle over the various ctrs and then switch to incremental, zero X&Y and then do the PCD using the incremental 0-0.

[Bruno TaylorParticipant @brunotaylor21701]

I had exactly the same problem for my first attempt at a number of holes on a PCD.  So l read the instructions again where it clearly said for a circle of n holes enter n+1 as the number of holes required. The DRO logic appears to be first and last hole in the same place. No probs since.

Edited By Bruno Taylor on 15/03/2018 17:45:27

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