What method to use in making part? Eyeball it or use the dials?

[Maplehead]

Please disregard the less than perfect slots and a couple mistakes here and there in the attached part pictured.
Anyways, this part I started out as a 4.28" diameter circle with two holes to hold the piece down while turning. The bottom 1/8" hole is one of the hold-down holes. The other got cut off as the final piece isn't a full circle.
My approach to making this piece was to scribe in black sharpie all my guide lines and then eyeball my center drills over all places for holes.
I was thinking of another approach which incorporates using a mill more technically, like I imagine the big boys do.
I would first cut the piece as a square and then find the edge and then use the dial numbers to move the exact x.xxx" amount from one hole to the next. I figure that this approach requires me hitting the TurboCad drawing and taking many measurements from a given starting point, true?
On the mill though, my worry on this approach has to do with lead screw backlash,(correct term?) or play.
I'm figuring that every time I turn an axis knob in the reverse direction I will be off from my original 0/0 start, meaning that all those measurements I recorded down from the Turbocad drwing will not transpose well on the mill.
Is this a correct concern?
What method do you use for making a part like mine here?

 

[T Bredehoft]

Once you set zero, and turn the handle either left or right, it will repeat when turning that direction. If you start turning it right, go to a position, make a cut, turn left back up an inch and a quarter, turn right again and go forward about a quarter, it will be accurate at that position. You won't have to go back to the original touch off point. Other than your worrying about reputability I'd do it probably the same way, although I use DRO on my mill. Go to position, [clamp the ways] make a cut [unclamp] go to the next position, repeat. Always clamp the axis you are not using. That's my advice, though I may not practice it 100 %.

 

[JimDawson]

I'm figuring that every time I turn an axis knob in the reverse direction I will be off from my original 0/0 start, meaning that all those measurements I recorded down from the Turbocad drwing will not transpose well on the mill.
Is this a correct concern?

No concern at all. Once you start the machining process, always approach the work from the same direction. So if you need to backup 0.125, backup 0.250 and then approach the work from the same direction. It's easier to do than to describe in words. You do it enough and you will automatically do it to compensate for the backlash. I still do it even with a DRO, it's just muscle memory.

What method would I use? I would just program it in. . Having said that, I have made lots of parts like that on a manual machine without a DRO, but I was machining long before DROs existed.

 

[RJSakowski]

I like to use ordinate dimensioning (dimensioning distance from a common reference point) because that is how the mill works. With a DRO, this is dead easy as I would set my DRO zero at the reference point and move to the positions on the print.

With a dial, it is a little more tricky since you have to keep track of the number of rotations as well. As Tom and Jim stated, you always want to approach from the same direct to account for any backlash but otherwise the process is the same. The DRO just simplifies the process since it displays the actual table position and backlash doesn't enter in.

If you are using a CNC where steps are counted to display the position, then backlash is again a factor. However, in order for a CNC mill to be useful, backlash has to be reduced to an acceptable level or corrected for in the controller software.

 

[RJSakowski]

There is another way to make repetitive features such as you have in your part, going by the dials. Make your first feature and rezero your dial and offset by the distance to the next feature. Move to the next feature and repeat the process. Its advantage is that if you have a weird distance like .137, you don't have to go through all the math additions to come up with the position. You still have to be careful about dealing with backlash and any rounding or other errors will stack up which is why I prefer the above method but it can give you an aesthetically pleasing pattern with minimal effort.

A third way which is used by woodworkers is to make a simple jig with a key which locates on the previously made feature and is offset by the spacing between the features. This can be a very efficient way to make a pattern and doesn't require any dials. For instance, it could be used to make a hole pattern using a drill press with a dowel pin to locate the previously drilled hole. A suitably made jig could be used to make a two dimensional array.

 

[T Bredehoft]

This may not solve your problem, but when I'm milling a slot, I use a smaller (than the slot) endmill, make a cut down the middle and one on each side to size. This eliminates to problem of the tool 'walking'.

 

[sanddan]

Great advise above.

The only thing I'd add is adding a DRO to your machines is a HUGE aid for a beginning hobby machinist. I started out using the dials as described above and it does work but I also had issues keeping track of where I was at. Counting turns of the dial and keeping track of the numbers PLUS all the other little details you are learning when just starting out can be intimidating. The DRO simplifies the learning process, one of the best upgrades I've done.

 

[3strucking]

Sanddan is right. My mill and lathe both have DRO and it has made the learning curve a lot easier. In my opinion a DRO would be the first thing Someone should purchase if it didn't come on a machine.

 

[Maplehead]

Hi All
Thanks for the reply.
I'd love a DRO on the mill but that'll be for some time. $$$
In the meantime I am going to learn old school and like it.
I'm not 100% on all the movements and math yet but I will draw up an illustration later with my questions that will hopefully be easily answered.

 

[BGHansen]

Couldn't agree more with RJ, sanddan and rightway1974. The best $500 spent in my lifetime was a 4-axis DRO for my mill. I "lost" it for a while this past winter as the shop got down to 20 F. Back to the dials . . . I use a hang tag on the handles labeled either "CW" or "CCW" to remind me which way I was turning when zero'ing out with an edge finder. Quickly grabbed a hair dryer to warm up the DRO, then left a heating pad on it. I'd rather deal with an occasional sore neck and no heating pad than no DRO!

Bruce