# DRO Arc Function



## jocat54 (Feb 22, 2017)

Spent some time today learning how to use the arc function on my DRO. Took a few trial runs to figure out where to start and stop at what angles (where 90*-180*-270* ect were). I sent it up for .050 cut, it took 17 steps to do one side--kind of rough finish. I guess if you set it up for smaller cuts you would have more steps and better finish. Pretty neat feature.


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## BFHammer (Feb 23, 2017)

Thanks for posting!  I'm anxiously awaiting the arrival of my first mill and love seeing what others are doing with theirs.

I'm trying to stretch my already battered tooling budget and one of the things I keep looking at but not buying is a rotary table. Just curious if you have one and if this is the type operation that could be performed with a rotary table also?  

Once you got the hang of the DRO process was it pretty efficient - say, how long do you think it would take you to cut an arc on the other end?

Please excuse the newbie questions!


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## ch2co (Feb 23, 2017)

Could you send a picture of your DRO screen? Where did you get it? It's not a CNC is it?
What mill are you using?


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## jocat54 (Feb 23, 2017)

ch2co, Here is a terrible picture of the DRO screen at step 2 of 17---you just zero both axis and move on to the next step. The mill is an old manual mill Grizzly 3616. I bought the DRO from Aliexpress (China) took about 10 days to get it. About $280. The other picture shows how rough the arc is at .050 cut.


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## Holescreek (Feb 23, 2017)

A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.




I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.




Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544


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## RJSakowski (Feb 23, 2017)

BFHammer said:


> .........Just curious if you have one and if this is the type operation that could be performed with a rotary table also?
> 
> Once you got the hang of the DRO process was it pretty efficient - say, how long do you think it would take you to cut an arc on the other end?
> 
> Please excuse the newbie questions!


You can cut an arc using a rotary table by setting the workpiece so the center of the arc is at the center of the table.  If you position the rotary table so that its center is directly under the spindle, you can fix your workpiece so a previously located arc center on your work is directly under the spindle.  Clamp the work and offset the table in the x or y direction by the radius of the arc plus half the cutter diameter.  Then make your cut.

This process could be made much easier by mounting an x/y table on the rotary table.  With a little mental math gymnastics, some fairly complicated machining could be done.

I have used the step and cut method with the DRO and it takes a fair amount of time to make the cut.  I usually used about 25 steps and it is tedious  process.  You have to be thinking about it during the entire process as the procedure involves moving first in one axis and then the other to the next coordinate.  Moving the wrong one first will  result in cutting into the part.  Then, when finished cutting, the scallops have to be smoothed by hand.  It works if no other option is available but it is one reason that I opted for a CNC mill.


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