Having problem milling 120 degree sections

[want2drive]

Good morning

extropic: here is the 67 degree test Gage and the original handle coupler half as apposed to the machine couple half which I re installed on the machine. see pictures. The fit looks to match as predicted. I don't want to get ahead of anything here so advise on my next operation is appreciated.

Flyinfool, IschgI99: I'm sure that exercise is easy for you and is something I want to do as it seems to be knowledge I need. I am not that good on CAD at the moment, that last exercise took me 4hrs to produce because I forgot all the commands and need additional hardware to be better at it. The pin measurement I am still studying the the formula to see what "csc" stands for in the equation. I know "a" is the angle but it looks like the "csc" is some multiplier of it or designation of it so I need to do my research but it's not on any of the diagrams. In the mean time I only have a short time before heading south so I need to proceed with something I know if I am to complete this project before I leave. In my last job, I left all the calculating to the engineers and contractors. Now, I am wishing I did some myself. Lazy I guess, you never know what the future brings, never thought I would want to do this back then.

Thank you

 

[extropic]

Ok, so it seems we're settled on 67° slots leaving 53° protrusions and about .040" for the offset.
Employ all safety equipment and procedures. If blood is drawn, I quit.

I'll try to outline a suggested order of operations:
Do the lathe work (face/drill/bore/turn/part) but leave the blank long enough to recut the coupling end if we miss the mark the first time.
Don't cut the blank to finished length or turn the OD for the handle fit until we get the coupling right.
On the mill, center the RT under the spindle and zero X and Y on the DRO. Do not lose these zeros. leave the DRO ON until the part is finished.
Secure the workpiece at the center of the RT.
I'm thinking you should cut the slots only about .05" deep (no point in going full depth) until we do a fit check.
I'm going to describe using X travel to make the cuts and describe them as conventional (not climb) cuts.
Rotate the RT to zero° on the RT scale and lock it.
Mount a .188" diameter 2 flute EM in your spindle.
Move the table (Y axis) away from the column (Y-) -.094"-.042" = -.136" on the DRO. I'm adding .002 to the offset to be a bit conservative.
You can cut it again if the .042 is too tight.
LOCK the Y axis travel.
Turn the spindle on and lock the spindle at about .050" depth of cut (DOC).
Start the cut by moving the table X+ (to the right) all the way across the workpiece.
Move the table/workpiece X-, back to the left of the spindle.
Rotate the RT to 120° and lock it. Repeat the same cut.
Move the table/workpiece X-, back to the left of the spindle.
Rotate the RT to 240° and lock it. Repeat the same cut.
Turn the spindle off but leave it on the X- side (left side) of the workpiece with the same DOC.
Unlock the Y axis travel and move the table (Y axis) toward the column (Y+) to .094+.042 = +.136" on the DRO.
Rotate the RT to 240°+53° = 293° and lock it.
Turn the spindle on (still set to about .050" DOC),
Start the cut by moving the table X- (to the left) all the way across the workpiece.
Move the table/workpiece X+, back to the right of the spindle.
Rotate the RT to 293°+120°-360° = 53° and lock it. Repeat the same cut.
Move the table/workpiece X+, back to the right of the spindle.
Rotate the RT to 53°+120° = 173° and lock it. Repeat the same cut.
There is a wedge shaped remnant in the center of each of the three intended slots.
Rotate the RT as required, lock the RT and mill those remnants off at about .050" DOC.
The fit check sample machining is completed, but leave it secured on the RT.
Deburr as required.
I'm recommending that you remove a hub (lead screw coupling half) from the machine and leave the workpiece on the machine so we don't lose our workpiece set-up and zeros.
Fit check a hub to the workpiece and let us know what you think.

 

[Huub Buis]

Place the original handle in the rotary table and you will see where things are going wrong. Don't drive the spindle and replace the cutter by a small rod of the same diameter.

 

[Flyinfool]

Good morning

extropic: here is the 67 degree test Gage and the original handle coupler half as apposed to the machine couple half which I re installed on the machine. see pictures. The fit looks to match as predicted. I don't want to get ahead of anything here so advise on my next operation is appreciated.

Flyinfool, IschgI99: I'm sure that exercise is easy for you and is something I want to do as it seems to be knowledge I need. I am not that good on CAD at the moment, that last exercise took me 4hrs to produce because I forgot all the commands and need additional hardware to be better at it. The pin measurement I am still studying the the formula to see what "csc" stands for in the equation. I know "a" is the angle but it looks like the "csc" is some multiplier of it or designation of it so I need to do my research but it's not on any of the diagrams. In the mean time I only have a short time before heading south so I need to proceed with something I know if I am to complete this project before I leave. In my last job, I left all the calculating to the engineers and contractors. Now, I am wishing I did some myself. Lazy I guess, you never know what the future brings, never thought I would want to do this back then.

Thank you

The "csc a" stands for cosecant of angle a. This is a trig function on most modern calculators. It is normally the 2nd function of the button labeled "sin".

 

[want2drive]

Thank you Flyinfool

My calculator shows Sin-1. I also looked up csc and got the definition and a few practice problems to illustrate the function. I will work through that and the pin method to broaden my knowledge on trig and more to the applications for machining. If you all haven't guessed yet I slept through those classes and life destroyed the remaining memory of what I learned by not applying it over my lifetime. I don't remember the last time I had to use any of this, but it has to be 40+yrs now. Sorry if I sound dumb, its just old age showing.

Thank you

 

[want2drive]

Good morning

Extropic: running into a problem before I get started.

Indicated the RT using a 3MT dead center this time around. Using the pointed dead center under the spindle I have .000” on the X axis and about .0005” on the Y axis. However, the indicator reeds “0” on the x axis and .001” on the Y axis. In other words each side of the Y axis is .001” using .0005” indicator and on the X axis it reads 0 on both sides. I proceeded thinking the difference would be under .0005”.

When I re installed the vise and tried to center the “Handle coupler half” under the spindle using the same indicator and not moving the mill table or the RT I have .002” on the Y axis and .0005” on the X axis.

Did that 3 times with the same results.

Prior to redoing the RT centering I tried to use the edge finder on the “Handle coupler half” and could not get centered. Thats why I went back and recentered the RT. It was off several thou. I’m glad I did. But knowing a bit more on centering things now, trying to figure out why its off and should I proceed.

The “Handle coupler half” that is in the vise has been turned and bored as described in the SOO.

Thank you

 

[epanzella]

For things that may take a few tries to get right. I often mill/turn test parts out of old 2x4s. Their somewhere between cheap and free for material, soft enough that you are very unlikly to break a tool, can be cut really fast, and you can just keep trying till you figure it out without breaking the bank in the process.

I use AZEK PVC trim boards for the same reason. Being a retired contractor I have a lot of it laying around. Cheap, easy to machine, and holds precise dimensions.

 

[extropic]

For those those following this tale, I have talked to @want2drive offline.
He has had his PM 932V for only about a month. It seems that some gibs need adjustment which has caused him grief trying to achieve repeatable readings. He is now cleaning and adjusting the X and Y gibs (maybe Z too).
Stay tuned for more progress.

 

[want2drive]

Good afternoon All

First and most important, I wish to thank everyone on this thread for their courtesy, professionalism and expertise. I was taught always to be humble, you all exhibit that trait and I am thankful. I'm sure some of you were typing and said to yourself, maybe not.

I would also like to thank extropic for his individual attention and assistance, big help, very grateful for that and his approach to troubleshoot the issues, including the "gibs".

As mentioned in the prior post some basic rookie errors were causing some major, to me at least, set up issues. I cleaned the machine when I received it and set it up but neglected to properly adjust the gibs to eliminate any table movement, found out the hard way what that causes.

So here is an update on my progress;

Following the SOO provided by extropic, I finally got to make the part I have been trying to make for the last 10 days or so. All went well and I think I understand offset, as related to this piece anyway. I had to redo it only twice, the calculations I gave earlier in this thread, were off a bit. The final offset was .141" as opposed to .136" in the SOO which translates to .007" from my original calculation. The pictures attached is the final "handle coupler half" that I will use to make the second one.

Unfortunately I ran out of time to complete these pieces as I have promised my wife to complete loading for the journey south.

I still have homework assignments that I need to complete, but for now, I have one machined part under my belt and I feel good about that accomplishment. Next season I will have more time to mess a few other parts up. Quill clamp for a tail stock DRO, etc.... cant wait.

Thank you all again, until next season, everyone be safe and enjoy the Holidays!

 

[extropic]

BINGO! Jackpot.

You're a winner. You asked for help, followed it, and made the necessary adjustments by yourself.

Drive safely.