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Old 03-28-2010, 11:20 PM   #1 (permalink)
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Post Machining Tips and Tricks

Hello Machinists,

This thread is for machinists, by machinists, and for machinists eyes only. It is a place to share tips and tricks of machining that you pick up over the years. It is a place to learn better ways of doing things that frustrate your very being. It is a place where all you troubles will be solved. This is the place that you give and receive great knowledge about machining. Share your experiences of what works and what doesn't work so others don't have to make the same mistakes and can find better ways of doing the same task.

Try to follow this format (it isn't necessary though)

Quote:
Task:
Problem:
Solution:
Comments:
I'll go first,

Quote:
Task: Grinding Internal O-ring Cutting Tool
Problem: Ground Tool flexes when trying to cut o-ring groove
Solution: Make the tool the biggest you possibly can while still fitting in the required hole. If you take away too much material, the tool WILL flex excessively.
Comments: I made this new grooving tool from a broken boring bar rod, It works quite well
Quote:
Task: Boring a Hole
Problem: Chatter
Solution: Slow the spindle speed and feed rate
Comments:
Quote:
Task: External Grooving
Problem: Chatter
Solution: Slow spindle speed. Slightly increase feed rate if necessary.
Comments:
Quote:
Task: Polishing Aluminum
Problem: Forgot the polishing compound at home, office, ect.
Solution: Use soap that has pumice in it. Gojo is a good example.
Comments: This produces a reasonable surface finish. Don't expect the same thing as true polishing compound though.
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Old 03-28-2010, 11:50 PM   #2 (permalink)
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There's already a pretty good forum for this...it's called Practical Machinist;

Practical Machinist - Largest Manufacturing Technology Forum on the Web
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Old 03-29-2010, 12:31 AM   #3 (permalink)
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Quote:
Task:Surface Grinding Stainless
Problem: Scorching
Solution:After truing the wheel use the diamond nib to dress a spiral into the wheel.
Comments:Rapid traverse or go really fast by hand to do this
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Old 03-29-2010, 01:13 AM   #4 (permalink)
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Old 03-29-2010, 11:54 AM   #5 (permalink)
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I'm used to working with metric values, but maybe some info can be of use.

Quote:
Task: Calculating spindle speed for milling (in meters per minute)
Problem: The official calculation takes too long!
Solution: Vc (cutting speed in meters) x 318 : diameter (mm) = RPM.
Comments: Simple calculation was shown to me by a mill salesman
Lets say you want to mill at 65 meters per minute with a 20mm mill: 65 x 318 : 20 = 1033,5 RPM

Quote:
Task: Drilling a metric sized hole prior to tapping
Problem: What size to use?
Solution: Diameter of the tap (in mm) minus the pitch (mm per revolution) is the drill size.
Comments: Drill hole slightly bigger in tougher materials if allowed. (0.1-0.2mm) Use cutting compound or coolant.
Quote:
Task: Boring low grade costruction steel
Problem: surface quality is poor
Solution: Increase radial chip thickness and if possible bore in one go to size.
Comments: coolant or cutting compound required
Quote:
Task: Milling hard plastics
Problem: Chipping
Solution: Use sharp tools, decrease feeds at corners, decrease cutting depth, change milling strategy. (climb milling is preferred, also look at entry and exit of cuts)
Comments:
Quote:
Task: Side milling
Problem: The mill is bending away so it's only to size on top of the contour
Solution: Try upcutting for the final pass
Comments: Not always succesfull
Quote:
Originally Posted by c6quad View Post
lefty loosey, righty tighty... lol
Quote:
Task: Left and righthanded threads
Problem: How to identify?
Solution: On the OD, seen from the side, Left threads start in the top left, and go down right... Right threads go low from left to high right.
Comments:
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Last edited by FiXeL; 03-29-2010 at 11:58 AM.
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Old 03-29-2010, 02:19 PM   #6 (permalink)
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the cutting speed formula in US is

4* cutting speed (in sfpm) / diameter

its actually (12*spfm) / (pi* diameter) but 12/pi is about 4 most machines just dont have the divisions to take into account the difference.
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Old 03-30-2010, 05:11 PM   #7 (permalink)
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Quote:
Task: Calculating Feeds and Speed
Problem: Getting it wrong
Solution: Use the chart, the chart is right
Comments: Not everyone believes this
...
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Old 04-01-2010, 04:25 PM   #8 (permalink)
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Quote:
Task: Hand Tapping
Problem: Not Concentric to turned part
Solution: Place the tap in the tail stock of the lathe. Set the spindle speed to as slow as it can go and turn on the spindle. Move tail stock close to the part but don't lock it down. Push tap into the hole to start the threads. STOP SPINDLE once you have gone about 2-4 threads in. You can now hand tap the rest and it will be concentric to the part. Or if you are comfortable, you can tap the whole hole this way.
Comments: Use some tapping fluid.
Disclaimer: Only try this if you are comfortable with it. You CAN break a tap by doing this (I personally never have but I have seen it done).

Quote:
Task: Sleeping
Problem: Not falling asleep fast enough.
Solution: Run for about 15 minutes before attempting to go to bed.
Comments: Might want to shower after the run though.
Quote:
Task: Sketching on Paper
Problem: Smudges
Solution: Use a clean piece of computer paper under your hand to prevent smudging.
Comments: Usually works if you don't move the paper with your hand.
Quote:
Task: Skecthing on Paper
Problem: Smudges
Solution: Start in the top left corner of the paper(if right handed)
Comments: Always works. But you have to visualize the whole drawing first or have an other drawing to reference.
Quote:
Task: Setting Tool Heights
Problem: How?
Solution: Use a piece of paper. Have the tool you want to set in the spindle. Bring the tool over the part. Place paper on part and under tool. Move paper from side to side while bringing the tool down in the smallest increments on machine. When paper stops moving freely or rips, then the tool is .002" (depending on paper used) above the surface of the part. Move tool away from part in the X or Y axis while keeping Z the same. Adjust the Z height to compensate for the thickness of the paper. This is your tool height for this part.
Comments: Usually works like a charm. If it doesn't, use next method.
Quote:
Task: Setting Tool Heights
Problem: How?
Solution: Use a parellel. Have the tool you want to set in the spindle. Bring the tool over the part. Bring tool close to the srface of the part. Place parallel on it's side on the top of the part. Slide parallel towards tool while raising tool. When the parallel slides under the tool, slide parallel out from under the tool and bring tool down a little. Raise tool in smallest increments while trying to slide parallel under tool. When the parallel does slide under tool, the tool is now exactly .125" (varies with the thickness of parallel used) from the surface of the part. Move tool away from part in the X or Y axis while keeping Z the same. Adjust the Z height to compensate for the thickness of the parallel. This is your tool height for this part.
Comments: Always works with flat top parts. Might not work with odd top parts.
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Old 04-02-2010, 12:00 PM   #9 (permalink)
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Quote:
Originally Posted by betasniper View Post
Task: Hand Tapping
Problem: Not Concentric to turned part
Solution: Place the tap in the tail stock of the lathe. Set the spindle speed to as slow as it can go and turn on the spindle. Move tail stock close to the part but don't lock it down. Push tap into the hole to start the threads. STOP SPINDLE once you have gone about 2-4 threads in. You can now hand tap the rest and it will be concentric to the part. Or if you are comfortable, you can tap the whole hole this way.
Comments: Use some tapping fluid.
This is NOT reccomended, specially if you actually require a "how-to" on it. all you are going to do is break a bunch of taps.

My reccomendation for tapping holes drilled in a lathe, or even on a mill/drillpress for that matter is this...

Chuck up some round stock in the lathe and whip up a small dead center w/ 60* taper (like your tailstock center), then turn it around and turn the other end down to a diameter that will fit in your jacobs (drill) chuck. You will end up with a little doohicky that looks like a round dradle.

(reserved for picture, maybe just of a dradle )

next; if your tap handle (t-handles for smaller taps) doesn't already have a hole in the end, chuck it up and center drill it.





When tapping, after drilling your hole just take the tap drill out of the chuck and put in the center you've just made. tap away, using the center to keep everything aligned and straight.





For larger taps, I make sure I only buy ones with center holes on the back of the tap itself, but if thats not an option you could also do up a center with a flat face, big enough to sit against the back of the tap handle. (this won't ensure alignment, but make it easier to achieve). And on the lathe, just pull the center or chuck or whatever you have in the tailstock out, and use the face of the shaft.




I got the tip to make up one of those centers from one of my first year instructors, and i think its something everyone should have in their tool box. Not being hardened it will wear out, but totally worth the time to make one up.
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Old 04-02-2010, 07:30 PM   #10 (permalink)
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facing off an overlength tube.

Task: Facing off an overlength tube.

Problem: tubing will hook and fly out of 3 jaw chuck

Solution: Insert proper diameter dowel inside tube (after center drilling dowel) and now you can face the tubing square. I do this all the time when making fake rainjackets (supressors). My lathe is only 3 ft long.

Comments: If one has a steady rest with roller bearings that would be ideal. Normal "brass contact" steady rest leaves marks on tubing.
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