SNS 310: Machining a Cast Iron Prism Straight Edge
ฝัง
- เผยแพร่เมื่อ 19 มิ.ย. 2020
- In this week's episode I machine a cast iron straight edge for my friend Lance. This is a raw casting that needs machined first, then Lance will finish it off by hand scraping to completely flat on all sides. I'll be using the K&T mill for the machining.
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maybe my computer but the music is louder than your voice
Looks like you screwed Lance.
still have a couple of Carver 12" rack clamps from my days in fabrication
Intrigues me every time I see this video
When Abom79 takes a "first pass" and it's instantly mirror smooth. 😅
Another problem with vertical mills and getting long things flat has to do with the ways of a ~5-ft~ long table only being supported by perhaps 24 inches of dovetail and gibs from below. As the table moves farther and farther to the right and left the weight of the overhanging table creates a fulcrum point at the ends of the lower ways and gibs. The ever-increasing weight of the long end of the table as it extends past the end of the lower ways lifts the shorter end. I.e. the table does not move on a horizontal plane, but in a very flat curve. As the vertical mill ages the lower ways wear more and more at the ends which contributes to the problem.
Could you lap it straight or is that too much.
Looking at the physics of the bar, two laws play in. 1. Mechanical - center support cuts the bending of the bar. 2. harmonics in the bar - the bar has a fundamental length and rings (sorta) when stimulated. That is flex going back to (1). You did two fixes - change the frequency (rpm) and cut the sympathetic oscillation in about half. One might get good results like you did by putting the support at 1/3 -2/3 location(s) mixing any resonant to be much higher and maybe beyond that of the bar. Complex maching sometimes. Think of the lathes that turned 30' cannon barrels for battleships. What a lathe an milling.
When you used the carver clamp on the 45 degree edge why did you not set the job on the small bee blocks you got and then you could have used three along the length?
It will make a great doorstop
Enjoyable viewing, I have the same caver clamps for my big mill. Great bit of kit. 👍🏻
Good idea to use the planer guage in the middle. What might help you inthe future is to set theplaner guage to the same height as your parallels. Then when you tighten the carver vise, set the planer guage in the middle as you did, but tighten the vise until the planer guage is as tight on the part as the parallels. That should help with the flatness. Another idea would be to machine all the faces, then go back and take a cleanup pass on each face. That should releive the stresses from the cast surfaces. Nice job!
on the slow speed filming, you could hear that the cutter was not exactly even with the surface. Great video capture.
👍👍👍
You did a splendid job, Adam, on cleaning up that prism. If you don't mind I'd like to suggest some things that might have helped you relieve the bow in the material.
@
when is shaper preferred over milling?
Some pro tips: a few minutes on the surface plate from the very beginning would help to identify geometric issues including bow or twist, map with a sharpie. These methods here make no considerations with these setups restraining and leaf properties of the raw cast stresses. Meaning this is only did a cosmetic descale, neglecting geometric integrity. It would have made more sense to just use a hand grinder.
Simply put can not cast anything without creating internal stresses. How you measure the internal stress is to slowly machine away surface and take deflection measurements. So the approach that you used to machine the prism guarantee that the surfaces would not be flat.
Ya the most important reason to use a stripping wheel on a cast part before machining is to get any sand out of the pits saves on mill tooling..does he sell those cast straight edges?