DRO -- Educate Me Please

[Bob Korves]

I've been pondering this while takingadvantage of good weather to get some yard projects done. I've decided I am getting a DRO and likely one of the lower cost models we have been discussing. I'm still struggling with scale sizing. According to the Bridgeport manual my mchine, with a power feed, has 16-1/2" of X axis travel, 12" of Y axis and 16" ofZ axis. I need to verify those numbers but assuming they are correct what would the scale lengths be. It seems most suppliers use a formula relating to travel + 140 mm. So do I just measure the travel, add 140 mm and order that scale overall length?

Thanks
Rick

To find the "real" travel, don't read the manual, move what you are trying to measure all the way to one end of it's travel until it stops, put a Sharpie mark across the interface between moving and stationary parts, move it all the way in the other direction until it stops, and then measure between the half Sharpie marks.

 

[Rick_B]

Thanks Bob - that's what I had in mond for verifying travel spec's from the manual.

Rick

 

[Bob Korves]

To find the "real" travel, don't read the manual, move what you are trying to measure all the way to one end of it's travel until it stops, put a Sharpie mark across the interface between moving and stationary parts, move it all the way in the other direction until it stops, and then measure between the half Sharpie marks.

Forgot to mention that you also need to move any stops, dogs, or other adjustable features that can limit the travel of the axis, out of the way or at least loosen them so they can slide. Make sure you are achieving the full travel possible for each axis.

 

[Kroll]

Robert I will be following your post here,if you will please let us(me) know what you order from who.There are so many choices out there it can/does give a person headache.Your questions and answers you receive has cleared up alot of ?marks in my head.So now I guess it comes down to who to purchase and what model from.Sounds like your budget and mine are about the same and I'm others as well.So we are not along on these issues,if I may also suggest to do a search on Youtube.There are several that I think is helpful on installing and what works for us guys that don't do this every day.Myself I am going close to pulling the trap off my BP and getting started on setting it up and install a DRO.Thanks for posting and asking some really good questions---kroll
I guess if a person keeps looking and researching you will find something else to ponder over http://www.star-techno.com/

 

[Rick_B]

I measured the actual travel on my Bridgeport - X = 17-3/4" (32" table with a power feed), Y = 10-1/2" (movement got very tight at back - I think the gib adjustment is too tight at the back side. I have another 2" or so of space so I'm going to assume Y = Bridgeport spec of 12"), Z = 16".

When I convert that to MM I get X = 451, Y = 305 and Z = 406. I saw on holescreek thread where he used 800, 350 and 450 for his 42" table machine and he mentioned that the X axis was about 12" longer than needed but it wasn't a problem. Right now I'm thinking I would order 600, 350 and 450 (X, Y and Z respectively). The question I have is that when I look at the offerings I typically see

Scale Length available

physical length is differnt from the travel length

50,100,150,200,250,300,350,400,450,500 ,550,

600,650,700,750,800,850,900,950,1000mm 5um.

physical length = 140mm + travel length

So if I want a 600 mm overall length what do I order - 600 - 140? Or is the statement above saying 600 mm scale will give you 460 mm of travel? I think I've got tunnel vision about this

Thanks
Rick

 

[Bob Korves]

Is there a good reason for ordering so much oversize? The main consideration beyond having enough travel is how and where you are going to mount them. Mock them up if necessary. You post does not show if the seller wants travel length or physical length to be supplied, or both. Make sure what they are asking for, and then make it very clear to them what dimension(s) you are supplying, keeping the language barrier in mind... Best is to use the exact nomenclature and sizing system (mm or inch) that they are asking for. Don't complicate things or it can and will get confused.

 

[Rick_B]

Bob - I am assuming when you question why oversize that you are referring to the X axis - the Y and Z are only 2 inches or so longer than travel.

Regarding the X - I was going off of holescreek's comment that a bit longer was not a problem and that it made locating the scale a little easier. Given that the cost is the same for the scales withing the range offered above - I'm wondering why a bit longer would be an issue for the X axis?

Thanks
Rick

 

[Bob Korves]

Bob - I am assuming when you question why oversize that you are referring to the X axis - the Y and Z are only 2 inches or so longer than travel.

Regarding the X - I was going off of holescreek's comment that a bit longer was not a problem and that it made locating the scale a little easier. Given that the cost is the same for the scales withing the range offered above - I'm wondering why a bit longer would be an issue for the X axis?

Thanks
Rick

My comment was more along the lines of "figure out where and how you want to mount the stuff and then order stuff to fit that plan."

 

[JPigg55]

Thought I'd post the unboxing photos of The Little Machine Shop DRO I spoke of before in this thread.
Added a couple shots of Yuriy's quadrature adapter too:

 

[Rick_B]

My comment was more along the lines of "figure out where and how you want to mount the stuff and then order stuff to fit that plan."

Bob - given that I have never seen a DRO in person (just internet pictures) and that I have no experience with mounting a DRO - its going to be difficult for me to figure out where and how it would be mounted. I was assuming that with a "standard Bridgeport" there would not be all that many options for mounting. X on the back of the table, Y on the saddle and Z on the frame next to the knee. I'm sure within those general parameters there are variations but I'm betting there are not a lot.

Without only limited knowledge of how a DRO actually works, I am assuming the scale attaches to a fixed surface and the reader head attaches to the moveable surface you are attempting to measure. Again - with a standard Bridgeport, the Y and Z are a given (I think) but the X has some variability related to table length. However, my thought right now is that as long as the overall length of the scale doesn't exceed the table length and is longer than the table travel then any length will work. I was hoping that someone who has installed a DRO on a Bridgeport could simply validate the X, Y and Z numbers I proposed above.

Thanks
Rick