Rotary Table Theory Question

[ChandlerJPerry]

Hey all, I have a question regarding theory of operation with a rotary table. Machine is a standard knee style mill. Here is a section view of a part I am interested in making that I designed (possible customer paying job, don't have full confirmation yet but trying to plan everything out in advance):




The bores are both 3 inches, although the upper bores are angled 5 degrees. I do have a tilting rotary table that I am planning to employ to aid with this. For the straight bores I planned on using some kind of 2 7/8" annular cutter/hole saw/etc to knock out the bulk of the material through the whole part while cutting the smaller ID, and then using an endmill with the rotary table to finish the bore, easy enough right? I figured I would do the same thing to finish the angled bores until I realized that the rotational axis of the table won't be aligned with the bore axis if the part is fastened flat to the table. Once the rotary table angle is set to 5 degrees, I wouldn't actually be able to make a circle with an endmill because the part would not be rotating about that bore, right?

Initial thoughts on how to overcome this are to use a boring head for the angled bores with the rotary table holding the 5 degree position. Definitely an option but kind of slow and fiddly, and I would be making four of these pieces total.

My second thought would be to make a basic 5 degree fixture plate/block that I could secure to the rotary table and then the part to that, in order allow the bore axes of the part and rotary table to align, and then go forward with my original approach using an endmill.

Third idea would be to employ a sine plate instead of a one off fixture in conjunction with the rotary table, although I don't own a sine plate (maybe a good excuse to get one?).

Am I on the right track here? Totally overthinking this? I would welcome any advice/feedback!

 

[GeneT45]

However you go about it, you need to tip the part in order to use the rotab for your angled holes. A sine plate (on the rotab) or a custom "wedge" would work. Of course it's got to be removed for the "straight" holes and machining.

GsT

 

[tq60]

A boring head would be a better choice.

Make a fixture that is flat on the bottom and correct angle on top.

If the top is made of disposable material, drill a hole at the center so easy alignment.

Sent from my SM-G781V using Tapatalk

 

[Just for fun]

Since you have four of them to make, make a fixture at the 5° angle, use a boring head and make your final cut. You won't need the rotary table for that operation. I think maybe I would make two fixtures, one for the bottom two bores and one for the angled bore.

At that point, once the fixture is in place make the two stright bores (both sizes) swap the part end for end and make the cuts on the second side. I would make all eight of the stright bores first then swap the fixture for the angled one.

I would use the rotary table for outside cuts.

Just an idea.

 

[ChandlerJPerry]

Thanks for the tips everyone. I think my trepidation about using the boring head comes from lack of experience with it. I do have a nice criterion boring head but haven't particularly needed to use it. I've watched videos on the usage and am confident with how to set up and operate it.

The thing I'm uncertain of is depth of cut on the boring head. Most material I've referenced refers to light cuts, .010-.020 or so. That's what caused my initial shy away from it, the idea of having to make 8-12 passes per hole seemed quite time consuming. My machine is around a 3/4 scale knee mill relative to a Bridgeport. Is it possible to take large roughing cuts or inadvisable due to chatter?

Possibly a large problem to add to my boring woes, is that my mill has no quill stop or power feed. I am worried that producing an accurate and decent finish bore without these things could be quite difficult, but I also don't have the experience to confirm that.

 

[Just for fun]

Thanks for the tips everyone. I think my trepidation about using the boring head comes from lack of experience with it. I do have a nice criterion boring head but haven't particularly needed to use it. I've watched videos on the usage and am confident with how to set up and operate it.

The thing I'm uncertain of is depth of cut on the boring head. Most material I've referenced refers to light cuts, .010-.020 or so. That's what caused my initial shy away from it, the idea of having to make 8-12 passes per hole seemed quite time consuming. My machine is around a 3/4 scale knee mill relative to a Bridgeport. Is it possible to take large roughing cuts or inadvisable due to chatter?

Possibly a large problem to add to my boring woes, is that my mill has no quill stop or power feed. I am worried that producing an accurate and decent finish bore without these things could be quite difficult, but I also don't have the experience to confirm that.

.010 to .020 sounds about right. Something I had to learn when machining is I had to be patient.

Getting an accurate depth might be a problem using the quill. If you make a fixtures for the bores, lock the quill and use the knee to come up to depth, you should be able to hit your numbers that way.

 

[ChandlerJPerry]

Why is the general preference for boring to use the quill? Ease of use with being able to set a stop I'm guessing? Also smooth finish if your quill is power feed equipped.

On the flip side I would think that moving the knee could be preferable for increased rigidity when the operation demands that. Although hand feeding the knee probably won't offer as consistent a finish as a power feed.

 

[Just for fun]

Your probably going to fine using the quill, your just going to have to go slow and easy and sneak up on depth as they say. At least on my mill I have both a DRO and the dials to get to my measurement. On my quill from the factory it only had a ruler, not vary accurate. I now have a 6" Shars DRO. You can get a clamp on quill stop for most mills.

https://www.amazon.com/Aluminum-Quick-Bridgeport-Milling-Machine/dp/B01A9J3INW

 

[ChandlerJPerry]

The clamp on quill stop is a great idea. I'll have to take a closer look when I get home today but I think it may not work due to the mechanism being enclosed, unlike a Bridgeport where it's out on the open.



My mill is supposed to have a fine downfeed with a graduated dial and handwheel, but aggravatingly someone in its past took a grinder to the gear teeth and rendered it nonfunctional. It would basically solve this issue if it were working, but I've yet to try and figure out a way to repair it.

 

[Just for fun]

Well that's a real bummer. I don't suppose there are any parts available either.