建造一个微型卡盘
A Miniature Lathe Chuck
A friend of mine collects small engines and machine tools. He recently got a small model lathe that
didn't come with a chuck, so I offered to make one for him. The lathe he got is a working model,
and not very big. He said a chuck of about 1" diameter would suit it well.
I started with the basic chuck body, which is mainly a round thing with a second smaller diameter on the otherend where the spindle threads will go. Here, it is shown next to my standard Taig four jaw independent chuck, andit will be built similar to that one. The Taig chuck is about 3.2" diameter, and the miniature for Kenneth will be 1".
You can see the threads inside the back side, and the part that has those threads comes out the back parallelto the front chuck surface, so that back part can be used for the needed chuck register. (The chuck registeris a part that is meant to mate up to the spindle and keeps the chuck true each time you take it off the spindleand then put it back on.)I stopped at this point to work on a new spindle for Kenneth's lathe. The spindle that is on his model lathenow has no register surface, so I want to make him one that does. Making a new spindle for his lathe willalso help me to get the new chuck made, as it will be handy to have something it mates up with in order toget the chuck running true. |
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3#
楼主|
发表于 2014-5-21 10:58:32
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In the pic above, I've turned down a diameter that will take the M12 x 1.5 threads, which is the thread on Kenneth'ssmall lathe spindle.
A bevel is put on the end that will take the threads to help start the die straight, and to make a nice startof the threads when they are completed. You can see here that I've center drilled the end of the piece. The otherend got the same treatment. The next step is to run the die over this part on the end. I didn't take pics of that bit.
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4#
楼主|
发表于 2014-5-21 10:59:10
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Now the piece is mounted between centers. The threads can't be seen here. They are under the two metal stripsnext to the drive plate on the lathe.
I've changed the drive clamp here because it was getting in the way. You can see that it's clamped on the threads of the new spindle. Both ends of the piece are supported between centers on the lathe and the final diameter for the new spindle is turned down. If you need top accuracy from your lathe on anything that is over a few inches long, the very best you can do is to turn between centers. Nothing else will be as accurate.In the olden days, before most of us were born, turning between centers was one of the only options.There were somewhat crude chucks back in those times, but they were not used when precision work was expected.Nowadays we have lots of work holding options for the lathe. Even more than most people know of, but still,turning between centers is the most accurate way.
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5#
楼主|
发表于 2014-5-21 11:00:02
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Here is the new spindle, along with the blank for the new chuck body.
One more shot, showing the chuck blank mounted to the new spindle.
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6#
楼主|
发表于 2014-5-21 11:01:00
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Now it's time for some serious work on the chuck body.I put it in my lathe chuck and checked the runout of the piece on my lathe, making minor adjustments untilI got under a couple thou on the runout. Then transferred my lathe chuck with the piece onto my small shopbuilt dividing head that had been squared up on my mill. Indexing the piece at 90 deg intervals, it was first spot drilled, then drilled for the tap size I wanted to use.
Then the four holes are tapped 8-32 for the adjusting screws that will move the chuck jaws. After tapping these holes, I removed my chuck from the dividing head to have a look at the progress. Screwingin four 8-32 screws I could see they were very slightly off center by looking in the hole in the center of themini chuck. Rats! Everyone makes mistakes. Everyone! I couldn't figure out how this happened, because Iwas quite careful while setting up the dividing head on the mill. It shouldn't be off! What happened was not a goof in setting up the piece, as I thought it must be. I found that one of the dialson my mill was slightly loose. I had just had the dials off to clean some crud that had built up behind them,and when I replaced them I had not got one of the friction rings tight behind one dial. Those dials tell you"where you are" on your mill table, and the one that I had not got tight had rotated on its own as I wascranking the table, giving a false reading. All my fault, but not in my setup work. In my maintenance work!Well, I got that dial put back on correctly, then re-checked all my settings. I didn't want to start over onthe piece, so I used an end mill to re-bore the holes for tapping. A drill bit wouldn't work, since they flex a lot and would have just followed the old hole crooked. I happened to have an end mill just the rightsize for a 10-32 tap, so used that and re-tapped the holes slightly larger. It worked out well in the end, asI decided the larger 10-32 screws were a better size anyway. A rare case of a mistake working out for the best. |
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7#
楼主|
发表于 2014-5-21 11:01:25
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Now I need to get set up to mill the slots in the mini chuck so it will take the four jaws. I have an adapterthat mounts to the rotary table so the table will take the chuck for my lathe. The rotary table and adapter arecentered under the mill spindle using a specially turned shank that fits tight through the adapter and into ahole in the rotary table. Then that shank is lined up so it fits tight in the spindle of the mill. The adapter is made by Taig. The rotary table is something I made here in the shop, and you canread about it if you like. Go to the main page link at the bottom of this page.
After mounting the body for the mini chuck in the four jaw chuck for my lathe, it is screwed onto the rotary table.
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8#
楼主|
发表于 2014-5-21 11:02:12
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To index the mini chuck so that the slots for the jaws will be at 90 deg, I put a brass plug in the chuckblank, then screwed in some long 10-32 cap screws. The brass plug lets the screws get tight, so they arepushed out against the threads in the side of the chuck body. This keeps them straight.
Then I can indicate off the shanks of the two screws, first on one side....
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9#
楼主|
发表于 2014-5-21 11:02:39
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....then on the other side. The rotary table is turned slightly one way or the other until I get thesame reading on each of the two screws.
First milling cuts go through the top of the chuck body, and down into the holes for the tapped threads.
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Second milling cut is with a larger end mill and makes a shallow recess in the top of the chuck body thatwill let the chuck jaws slide across the top of the chuck without wobbling side to side. The jaws will be the same width as that top slot.
Then the rotary table is turned 90 deg and the same thing done again. There is more to do to finish the chuck body.
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For the next step on the chuck body, I need to cut a slot inside the chuck kind of like a T-slot. Usually, for a tool to make a cut like what I need, I just make the tool out of drill rod (silver steel),then harden it and hone on the cutting edges. For the tool here I'm trying something different. Insteadof making a complete tool, I'm going to try grinding an end mill to the shape I need. A while back I bought a lot of 10 cheapo Chinese end mills. They are brand new, but after trying oneI find they are quite inferior for making a good finish, so I've only used one of that lot of 10, andthe rest I tossed into a junk box. I'm not happy with them at all! I figured I have nothing to loosein hacking up a new one of these to see how it does for this job.This involves grinding down the end mill flutes in the lathe. I covered the lathe bed with tin foilto protect it from the abrasive dust made with the grinding wheel. Then I got after it with the Dremel.The lathe was run at a couple hundred RPM and the Dremel was set to 5000 RPM. Safety glasses on, andstart grinding.
When I got done with it, I had this thing, which is shaped much like a T-slot cutter, 3/16" diameter and.055" wide. It only took about 10 minutes, which is a lot faster than making the tool from a drill rod blank.After I was done, I completely disassembled that chuck on my lathe and cleaned it in solvent. Cleaned thewhole lathe, too. I do not like grinding on the lathe. The dust gets everywhere and it's very abrasive.Bad for bearings, lathe ways, scroll chucks, and all that.I would never do this on my Atlas lathe. It has exposed bearing ends and I'd have nightmares about it. The Taig lathe has sealed bearings, but it still bugs me some. It's a normal thing to do on a lathe forhighly finished things like camshafts, or even a lathe spindle. I'm not saying you shouldn't do it, butyou must clean up after yourself very well afterward if you want your machines to last.
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