How to mill curves on rotary table

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kevincoxshall

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Hi I am relatively new here.
I am ok cutting striaghts on the mill but I would like to know how to cut a radius using a rotary table. I have seen the method where a drill bit goes through a hole and the curve is cut by moving the work by hand. This seems rather dangerous to me, and how do you ensure accuracy where the curve meet the straight section? Is it just judging it by eye?
I am trying to make a steam gland that involves 2 different radius'
Thanks for any help.
Kevin

 

cidrontmg

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Yes, it seems dangerous (and it IS somewhat dangerous ), but it can be done quite easily and safely. Make sure that the drill bit (or whatever pivot you´re using) is a tight fit in the hole, make sure that the workpiece rests on a solid flat horizontal surface, and make sure that you can hold the workpiece firmly without getting your fingers very near the cutter. If need be, use an extension. And you can easily see and hear when the cutter is moving close to the straight area. And work slow, very small cuts only. The process is far less dangerous than you would imagine before you try :)
Of course you can do the same with a rotary table, but you are likely to need some sort of a support (a jig, if you will) to hold the workpiece. Doing it "freehand" is way faster for a one-off, but if you plan on making many similar pieces, that might justify building a jig for the rotab.
 

b.lindsey

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Kevin, assuming you are making this from bar stock I would rough it out using straight cuts (see attached .pdf) and then remove the hatched areas on each end. That would leave minimal material that has to be removed. At that point you can consider using a small drum type sander instead of a cutter still using a drill or post through the hole and rotating it by hand. If this part is small, as I suspect it is, its will be hard to get a firm grip without being close to the cutter, so you may want to think about pliers, vise grips, or other holding methods as well. All in all though I find a drum sander much less intimidating (not to mention safer!!!) than using a milling cutter, especially on small parts. Glands usually aren't that critical as far as the outer contour so even some careful hand filing might be enough once you remove most of the excess material. Hope this helps

View attachment Gland.pdf
 

gbritnell

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Hi Kevin,
Here's what you need to do.
1. Mount your rotary table.
2. Depending on the type of mill, round column or knee, provide enough head space to indicate the center of the rotary table and still get a cutter to the workpiece.
3. Mount your part. If the part is irregular shaped sometimes it's easier to make up a mounting plate to fasten the part to. This way you can move the part to center and then clamp the plate in place.
4. Indicate an existing center on your part, hole or layout line.
5. Once on center zero out your dials.
6. For a part similar to what you're showing you will also need to have a layout line that runs across the piece. Once you have the part on center square up the layout line by rotating the table as you move from end to end on the layout line. (with a wiggler)
7. Once you have the job squared up mark where your rotary table is positioned or move your reference pointer to an even degree mark.
8. Insert the cutter of choice. A larger diameter will give you a smoother cut.
9. Move one axis off center and then move the table back toward the part until the cutter starts to cut. Before you cut you should know what calculated degree of angle you will need to stop the radius at. This will be the blend point between the radius and the straight wall.
10. Start cutting your radius. Generally I stay about 1/2 degree away from my tangent point until I get the radius to where I want it. This will prevent the cutter from digging in and leaving a mark where the tangent point is. After you have the radius milled rotate the table to the appropriate angle and mill the straight sides. There will be a small amount of stock where you stayed shy of the angle when cutting the radius.
11. Now for your final cut, rotate the table so that your straight cut will be a climb cut. Take a finish pass along the straight wall until you axis dial reads -0-. Rotate the table the required amount until you get to the other tangent angle, lock the rotary table and then make your final straight cut.
12. You should now have a nice smooth, seamless cut from one flat to the radius to the other flat.
13. If you have the part mounted to a plate where you don't have a clamp in the way, rotate the part 180 degrees and do the same for the other side.
14. A light touch will a file and some emery and you have a finished piece.
gbritnell
 

Jasonb

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Kevin, have a look at the last thread in this post where I show machining a boss to take a similar fitting to a gland, the only difference is that I would hold the part in a chuck on the rotary table like this

Jason
 

tel

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By the time you fool around setting up the r. table and jig/chuck, you could have had them done with the use of filing buttons and files. These are crank arms, but the same principle applies





 

kevincoxshall

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Thank you for all the advice.
Here is what I have done so far............



I am planning making 2 out of this lump. 1 to silver solder onto the plate, and drill it once lined up with the bore.
 

tel

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Certainly looking good so far - it would be very easy to file the profile from that point, but that's just how I would do it.
 

bearcar1

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Not having a RT I have to agree with Tel, it would be so much simpler to use filing buttons, not to mention it would probably be a bit faster as well. Here is the series of photos from a build I did a while back showing the bits being made into glands similar to what you are wanting to do.

BC1
Jim



a.jpg_thumb.png


b.jpg_thumb.png


c.JPG_thumb.png


d.JPG_thumb.png
 

GWRdriver

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As we see from almost every similar thread everyone has their own way of doing things. First off, I prefer an oval gland face but as always the shape is up to the individual. I start with a lathe turned gland blank on which the face is usually a full disk. Sometimes a scrap of material will just make a gland and then I have less than a full disk. To finish the face I first indicate from the rod bore and drill the gland stud holes in the mill. Next I lay out a true oval (with stud circles) on CAD and glue the paper printout to the face of the blank face, using the stud holes as locators. I then free-hand mill or grind all but a tiny bit of excess material from the perimeter. I finish off with all hand work, a combination of fine grit belt grinder, filing buttons, and files.

GLAND3.jpg
 

Artie

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tel said:
Certainly looking good so far - it would be very easy to file the profile from that point, but that's just how I would do it.
I believe that we sometimes go a bit overboard with our machinery, just because we have the latest Acme XYZ Super Duper Watsit doesnt mean our files are redundant.....

As the Boy From Bathurst (Uncle Tel) has said here, hand tools are a big part of our hobby.... dont forget them.... yes looking good so far...

;D
 

Jasonb

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Must say my usual method is to round around the stud holes with buttons but as I'd seen this question thought I would do it all in the mill. It was actually very quick, just loosen the vice fron the RT until the stud hole was central using a pointed peg in the stud hole and tighten up teh vice and mill away.

I usually prefer the straight sided flanges and in this case the prototype has this shape so oval would not look correct.

Jason
 

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