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torker
04-25-2005, 12:50 AM
Hey guys! I've just finished the last of the bolt circles for a project. Did them all on my lathe indexer.
With a lathe you are limited to the swing size. With a mill you could do much bigger circles.
Some of you have mentioned doing these with a DRO.
I'm assuming you use bolt pattern formulas for the movement of the positions around the circle.
Would you start in the center, go out to your first hole and continue around or do you do holes directly across from each other (on an even numbered pattern)and then position for the next one and go across to the opposite side again?
I'm betting you could do some pretty large stuff on a mill with some imagination. Thanks!
Russ

3 Phase Lightbulb
04-25-2005, 01:15 AM
Drilling bolt holes with a DRO is great... I made a sprocket using a Bridgeport and a DRO, and a simple Sprocket program I wrote that just printed out a list of X,Y positions that I used to make this sprocket:

http://www.bbssystem.com/projects/sprocket.jpg

Just make sure you move to your X,Y position, then lock the table in X/Y, drill, unlock and continue to your next hole.

-Adrian

tattoomike68
04-25-2005, 02:38 AM
this pipe flange was to big to use a dro http://bbs.homeshopmachinist.net//frown.gif

I would have loved to not haul that heavy table with a 10" chuck onto the mill, then put that 25" x 1" plate circle on top of that. (as you can see I was too lazy to pull the vice)

http://img.photobucket.com/albums/v488/miketattoo68/bigpipeflange.jpg

torker
04-25-2005, 06:33 AM
Nice stuff guys! Makes the price of a DRO look a little better when I see that.
Ha, it also reminds me that I need to mount the chuck on my rotary table.

Forrest Addy
04-25-2005, 07:03 AM
Sorry to jump at you Tattoo, but here's a lesson for milling machine users to draw from.

Look in Tattoo's photo how he's loading his Bridgeport table and saddle with all that weight off to one side. The overhung weight puts a big strain on the saddle dovetails. Dovetails don't like eccentric loading. The overhung weight trys to pry open the DT's producing unit loads far higher than a casual guess you estimate.

That's why turret mills have the turret and ram - so you can center heavy table loads and move the head almost anyplace you need to in the work envelope. If in Tattoo's example you swing the turret over about 10" and extend it a bit you can put all that weight over the saddle. With the weight centered you can do all your machine work and drilling off to one side.

I know Tattoo isn't moving the table or the saddle around much to drill and bore that hole circle but eccentric loading of a light duty machine is a bad habit to get into.

I watched a BP worn to a rattling frazzle in less than 7 years thanks to eccentric loading from boring hydrant silver braze preps on a 10" 4 way fire main casting. The machine was practically dedicated to this job because of the swivel and knuckle of the head. They put a 15" K&T rotary table on the center of the table, then plunked that 200+ lb hydrant casting down on it for indexing the 4 nozzles. They dialed off center (almost to the end of the table travel) to get at the nozzle with the head tipped 45 degrees.

On swingshift one weekend I took over the job, worked out the solid trig so the load was centered over the knee. Then I swiveled the turret to the right and tweaked the nod and tilt to produce the 45 degree boring axis along the table needed to bore the hydrant nozzle. Next time I saw the machine it was restored to the original way-off center set-up and the guy who "owned" the machine glared at me for daring to disturb his perfect set-up. What can you do?

After a few years of this abuse you could snug the table clamp and jerk the table ends by hand to get VISIBLE rotation about the yaw axis as you listened to the oil slurp in the dovetails. How do I know all this? I'm the guy who did the machine work to rebuild it. After machining and scraping it took a 0.063 shim behind the table gib to restore it to adjustability.

[This message has been edited by Forrest Addy (edited 04-25-2005).]

wierdscience
04-25-2005, 08:17 AM
Russ most of the better DRO's have bolt circle programs built in.You can start from one edge of a part or the center of the pattern.

Shop down the street had an Accurite that would do any count up to 199 holes.Real nice if you need to make the odd indexing plate for the dividing head.

Forrest,glad you brought that up,I agree several places I have seen the knee load on a b-port is supposed to be limited to 150lbs.

A 6" mill vice takes up half of that so your left with 75lbs usable limit.Once and awhile if the load is centered doesn't hurt much.But if it's a day in day out job I was taught to use a bigger mill.

Forrest Addy
04-25-2005, 12:15 PM
Answering your question.

x coordinate = sin((#/n) x 360) x rBC

y coordinate = Cos((#/n) x 360) x rBC

# = the hole number you're working on

n = total number of holes

rBC = the bolt circle radius

It's best to work out a spreadsheet in MS Works or equivalent and print a list of coordinates. If you're handier with a calculator then use the trig functions etc to make a list of hole coordinates. Hole circles evenly divisible by 4 require a list only for the first quadrant. By 2 requires the first semi-circle. By 1 requires a full circle's worth of numbers.

Make the coordiante table at your liesure where you usually do your paperwork not at the machine where there's no surface to sketch and draw on.

The next trick is to dial off the coordinates with out transposing a two digits, dialing off an x for one hole then the y for the next hole down, and similar blunders which my scrap bin has concealed at one time or another.

mklotz
04-25-2005, 12:24 PM
Forrest,

Or the mathematically challenged can download BOLTCIRC from my page and use it
to produce a printable file that looks like:

---------------------------
Boltcircle specification:
Radius of bolt circle = 1.0000
Bolt hole diameter = 0.5000
Spacing between hole edges = 0.6756
Angular offset of first hole = 0.0000 deg
X offset of bolt circle center = 0.0000
Y offset of bolt circle center = 0.0000

HOLE ANGLE X-COORD Y-COORD

1 0.0000 1.0000 0.0000
2 72.0000 0.3090 0.9511
3 144.0000 -0.8090 0.5878
4 216.0000 -0.8090 -0.5878
5 288.0000 0.3090 -0.9511
---------------------------

Regards, Marv

Home Shop Freeware - Tools for People Who Build Things
http://www.geocities.com/mklotz.geo

3 Phase Lightbulb
04-25-2005, 12:29 PM
<font face="Verdana, Arial" size="2">Originally posted by Forrest Addy:
Answering your question.

x coordinate = sin((#/n) x 360) x rBC

y coordinate = Cos((#/n) x 360) x rBC

# = the hole number you're working on

n = total number of holes

rBC = the bolt circle radius

It's best to work out a spreadsheet in MS Works or equivalent and print a list of coordinates. If you're handier with a calculator then use the trig functions etc to make a list of hole coordinates. Hole circles evenly divisible by 4 require a list only for the first quadrant. By 2 requires the first semi-circle. By 1 requires a full circle's worth of numbers.

Make the coordiante table at your liesure where you usually do your paperwork not at the machine where there's no surface to sketch and draw on.

The next trick is to dial off the coordinates with out transposing a two digits, dialing off an x for one hole then the y for the next hole down, and similar blunders which my scrap bin has concealed at one time or another.</font>


Actually, your equations are completely wrong...

Here is the correct equation:

PI = 3.1415926

thetaDelta = ((PI * 2) / numberOfHoles)

X position = Cos(n * thetaDelta) * radius
Y position = Sin(n * thetaDelta) * radius

Where n equals 0 to numberOfHoles-1 and radius is diameter of your hole pattern divided by 2.

For additional information, and an example, you can see my sprocket/bolt hole program here:

http://bbssystem.com/viewtopic.php?t=148

-Adrian

tattoomike68
04-25-2005, 01:11 PM
Forrest Addy you are 100% right. I did have a dead man and screw jack under the table before the picture (I was tearing it down)

that machine is bigger than it looks (10x50 table), it get all kinds of stuff that makes that look like nothing , big cat parts, 1" keys in rock crusher shafts, motor blocks, big machine walking beams,saw mill head shafts.(things im sure you have done too)

It is our "beater" mill, every shop needs one. we need to drag it over to the welding side of the shop and let it be the welders drill press. http://bbs.homeshopmachinist.net//smile.gif

precisionworks
04-25-2005, 01:21 PM
Russ,

As Weird mentioned, see if your DRO has the bolthole program. My Accurite does. All you do is center the part, input the hole radius & number of holes, and follow the DRO to zero-zero.

I usually start the first hole at three o'clock (directly right of dead center by an amount equal to the radius of the circle). There are other options in the program.

Takes a lot longer to dial in the center than it does to program the pattern.

------------------
Barry Milton

rfrey
04-25-2005, 01:34 PM
<font face="Verdana, Arial" size="2">Originally posted by 3 Phase Lightbulb:

Actually, your equations are completely wrong...

Here is the correct equation:

PI = 3.1415926

thetaDelta = ((PI * 2) / numberOfHoles)

X position = Cos(n * thetaDelta) * radius
Y position = Sin(n * thetaDelta) * radius

Where n equals 0 to numberOfHoles-1 and radius is diameter of your hole pattern divided by 2.

For additional information, and an example, you can see my sprocket/bolt hole program here:

http://bbssystem.com/viewtopic.php?t=148

-Adrian</font>

Forrest's equations are sound. You converted the angle to radians with the 2pi, then back again by muliplying by the radius. That's appropriate because your C program uses the math.h library, whose trig functions take radian arguments.

Forrest used degrees (#/n * 360 = degrees of the angle), which is much more appropriate for folks using pocket calculators and/or spreadsheets.



[This message has been edited by rfrey (edited 04-25-2005).]

precisionworks
04-25-2005, 01:58 PM
That REALLY makes me appreciate the bolthole program.

torker
04-25-2005, 03:29 PM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
Russ most of the better DRO's have bolt circle programs built in.</font>

weird...That's why I asked the question. I'm starting to figure out the milling machine package I want and was not even aware that there where programs built into the DRO's. I guess yer sayin to let a few more moths out of the ol' wallet huh? (quite a few more actually...lol!)

Barry, I think I likey the bolt hole program now also!
Thanks for ALL the info guys! I'm starting to see a DRO as a must, MUST have now!
Russ

Randy
04-25-2005, 04:09 PM
Machinery's handbook has bolt circle tables which you might find helpful. Personally, I'd either calculate them, or work them out on Mastercam.

Bill Neufeld
04-25-2005, 04:10 PM
Russ;
I have a BP + clone at work with the Accurite Millman package installed. The dro have the features for doing this type of work. You should check the other makers specs for the same features.
The basic units do not generally include these features.
Take care:
Bill

Forrest Addy
04-25-2005, 04:47 PM
Adrian: Degrees. Radians. You picks yer angular units and your works yer problem accordingly. As rfrey pointed out the degrees formulae I posted works handiest with the trig capable pocket calculators 95% of which don't have trig functions of radians.

I concede radian angular measure is handier in scientific calculations but of NONE the machine tools I've ever worked with in my whole life had angular scales graduated in radian; always degrees. It seems kinda silly to convert to radians when no machine tools or angular measurement tools read in radians.

I dunno. Let's take a poll. How many of you guys have compounds, rotary tables, and protractors graduated in radians?

[This message has been edited by Forrest Addy (edited 04-25-2005).]

ibewgypsie
04-25-2005, 04:56 PM
Mach3 has a wizard, you type in the circle diameter, the number of holes, Select peck stroke or? the feed rate and push "GO". It writes the code for you, (and you open the fridge over the Leblond and get a beer).

It alone was worth the price of the machine, Mach3, and space and time it took to put it all together.

COOL... Home shop cnc.. saves me time. Art did a lot more Work than I did to make it happen (ART of Mach3 author)

Paul Alciatore
04-25-2005, 05:04 PM
The easy way to get X-Y coordinates for a bolt circle is to do a CAD drawing and dimension it with Ordinate dimensions. It only takes a few minutes and any CAD program will be far more accurate than any machine you or I have or will have. You don't need to do the entire part, just the circle, it's center and the centers of the holes. Use the center of the circle as your zero point when dimensioning for easiest set-up on the mill.

The CAD program does the trig.

Oh, and you don't even need the DRO, the dials should be good enough for most purposes. I've done it that way and it is quite easy and accurate. Just be sure to approach each location from the same direction to eliminate backlash (that's lost motion for you guys across the pond).

Paul A.

[This message has been edited by Paul Alciatore (edited 04-25-2005).]

mochinist
04-25-2005, 07:35 PM
Torker: When you get around to buying a dro, save your money and buy a newall brand dro. They have the bolt hole circle function built in and are the best dro for the money. You can get a cheaper one with a glass scale, but I am thinking from your other post that this will be used for your business. My company installs probably 10 to 15 newall dro's a year, we have no affiliation and get no kickback from newall for doing this, we won't install anything else. In the 5 years that I have worked at my job we have only had to replace one scale and this was because the company managed to hit it with a forklift somehow, newall replaced it for free, and the company only paid us labor for the replacement. We get calls all the time from people with glass scaled dro's and it is usually cheaper to just replace the dro or we tell them to look on ebay if they don't want to do that. If this is for your homeshop and money is a issue, then by all means go with whatever you can afford, but for reliability and a business go with the newall.

I by the way never use the bolt hole function on the dro, I have the formula's for up to 12 bolt hole's on my toolbox and it just takes a sec, anything higher than that or even lower sometimes I use the CNC or plot it out with the cad program. My handwriting is messy and I would rather have a nice computer printout that I can read clearly.

wierdscience
04-25-2005, 08:12 PM
I like Accurite,Newall and Sony.

Accurite's repair service sends you a loaner and a UPS pickup slip when the monitor acts up(only once in six years after a lightning storm)

Newall,well I like the're scales,they are topps.

Sony,most things Sony makes are good so are the DRO's.

The one I like but haven't tried are the Mitutoyo absolutes.They are down to $700 for a three axis mill package.They don't have the bolt circle feature,but most of us have patterns we use over and over.I calaculate one and then write it down in a notebook for quick retrival in the future.

torker
04-26-2005, 12:51 AM
Thanks for all your time guys! I appreciate the informed info...as usuall it saves me from making dummass mistakes. Well MOST of the time anyway. I'm going to have to talk to a couple of dealers and see who will throw out the best deal. Thanks again.
Russ

[This message has been edited by torker (edited 04-26-2005).]