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Looking for a tool to profile and make bottom flat.

#40fan

Plastic
Joined
Jul 5, 2020
Working on a manual lathe and I have a part to make. I'll post a paint drawing of what it sort of looks like, but the biggest issue is the diameter at the bottom and needing to be flat.

I have an indexable drill that works down to 10mm, but that is as small as I have been able to find. With the .282" size at the bottom, having the tool being able to profile the taper down to the flat is likely a must as well.

The flat being right at an inch in depth is the next issue.

I've made a couple test samples out of aluminum with a 1/4" 2 flute end mill that left a bad finish on the profile of the part. When I switch to the final material, 304SS, I'm sure that won't work.

Any suggestions?

Cut.jpg
 
Just one? Rough it out with 2 or3 drills, set the compound to your angle and finish it with a small boring bar.
 
How could I possibly make a suggestion when I don't know if this is a round hole in the end or a groove around the OD? And you say the flat is about 1" deep, but the sides are only 0.005" long? It just does not compute.

I think you need to post that drawing or a photo.
 
If I understand correctly that you're making a flat-bottomed cone with a .500 large diameter and a .282 small, and you set up a 1/4" endmill in a toolholder on the compound of the lathe to bore the taper, that sounds like the same approach I might take to cut it manually.

But be aware that on most manual lathes the compound does not have as good linear accuracy or stability as the cross slide. They're simply too flimsy and less stable, and it's easy to leave ridges behind when using a sharp-pointed tool like an endmill as the boring bar.

If you ever run across a loose Hardinge compound and it can fit your lathe, buy it and adapt it, they're typically much more precise that most other small machine compounds. Or, you can "blueprint" your compound, but it'll take either proper grinding on a surface grinder, or scraping (and learning that if you don't already know how).

In the meantime, if you can stand a little extra work you could make a male plug a little smaller than the final taper size, and wrap the cone with some fine sandpaper to act as a finishing lap. Frequent replacement of the paper will be needed, so cutting strips that are pre-sized will save you time, as well as using a light oil to lube and clean the sandpaper in use.
 
If I understand correctly that you're making a flat-bottomed cone with a .500 large diameter and a .282 small, and you set up a 1/4" endmill in a toolholder on the compound of the lathe to bore the taper, that sounds like the same approach I might take to cut it manually.

But be aware that on most manual lathes the compound does not have as good linear accuracy or stability as the cross slide. They're simply too flimsy and less stable, and it's easy to leave ridges behind when using a sharp-pointed tool like an endmill as the boring bar.

If you ever run across a loose Hardinge compound and it can fit your lathe, buy it and adapt it, they're typically much more precise that most other small machine compounds. Or, you can "blueprint" your compound, but it'll take either proper grinding on a surface grinder, or scraping (and learning that if you don't already know how).

In the meantime, if you can stand a little extra work you could make a male plug a little smaller than the final taper size, and wrap the cone with some fine sandpaper to act as a finishing lap. Frequent replacement of the paper will be needed, so cutting strips that are pre-sized will save you time, as well as using a light oil to lube and clean the sandpaper in use.

Yes, that is exactly it.

I have no issues with the compound other than trying to use the end mill as a cutter. Probably the radius of the corner making the finish junk. If I were to use a boring bar, finish would be fine, but getting to depth and having a flat bottom, without running the boring bar into the opposing taper, is the issue.

The indexable drill that I have that is 10mm has two square shaped inserts that has worked perfect for a very similar part, but with just a larger bottom diameter. Hoping there was something out there that I couldn't find that you guys would steer me too.

@jancollc Stiff and small enough boring bar to get it done? I wouldn't mind hitting the bottom with a flat faced bit/end mill if I could fit a boring bar in there without contacting the opposing taper.

@EPAIII Sorry I didn't make the pic clear enough for you. Shitty paint drawing to begin with, but I'll add another with correct orientation with more detail. :D

Crap.jpg
 
...@jancollc Stiff and small enough boring bar to get it done? I wouldn't mind hitting the bottom with a flat faced bit/end mill if I could fit a boring bar in there without contacting the opposing taper.
I have several miniature boring bars from Kennametal with 3/16 and 1/4" shanks.

If the compound is set at your angle, you would be able to bore to your depth and use the cross slide to feed across the face to center.

I's a small tool, you aren't going to be taking heavy cuts. This one is a EO3H-SCFDR1.2

boring bar.jpg
 
First I would make an accurate CAD drawing. Paint sucks for mechanical drawing. And there are enough inexpensive and free 2D CAD programs out there to give you a great selection. (I use FastCAD, but it is not free. It does have a generous, free trial period and I found it easy to learn.)

That CAD drawing would provide two critical things: the angle for the cone and the amount that you will have to grind off of the back side of a boring bar so that it will not interfere.

Yes, I would use two or more drill bits to rough it out. The CAD drawing, with the addition of parallel lines to represent the drill bits will also provide the depth that can be safely drilled with each of the bits you use.

A 1/8" (0.125" diameter), end cutting, end mill will give you a good start on the flat bottom. But leave a few thousandths for a finish cut with a boring bar.

I would grind a boring bar with enough back side AND BOTTOM clearance ground to allow it to go to the full depth of the cone/bottom interface. Those inexpensive sets of carbide tipped boring bars would be a good source of a short one for this. I have about 1 3/4 of those sets and they are a great source for expendable tools like this. I would not try to include the angle to the bottom on this cutter: just leave the tip"s angle at 90°.

I would grind another boring bar for the bottom. It would have a straight nose and a small radius on the right side but a sharp 90° corner on the left. That way you can go to the full depth at the corner between the bottom and the conical side while having a radius on the corner in the direction of the feed. This boring bar would have a tip that is about 0.050" or less wide, so that it will have to be feed across the bottom to create the final, flat there. It can have an obtuse angle on the right corner to provide more rigidity. But this angle should not allow interference with the cone and again, don't forget the clearance on the bottom.

Another concern is that sharp corner at the OD. That is going to be hard to create with any measure of precision. If it can have even a short flat it will be a lot easier. If you can not do that, then I would use larger stock and turn the OD after this divot on the end if finished.

As for a lack of rigidity in the compound, that may be due to undesired movement in the carriage or cross feeds. I would LOCK both of those down while making each cut in this process. Also check the adjustment of the gib screws on the compound before starting.
 
.282 a K drill would do that size (.281). Drill K to almost depth and then grind off the drill end and make a flat bottom of it and drill-bore to depth.
Set the compound to angle, looks like about 6* or 6 1/4 degrees and go in and out on that angle with a home made tool bit that has a >1/4 nose and cuts on its left side (made like a boring bar).
Clearance under the cutting edge has to fall away to clear the id (clear s 1/4" ID)

Good to pre-drill with a 1/4" drill so the K drill does not run oversize.

RE: Remaining.109 x 1" so trig that out to get angle...looks like around 6* or so just rough sketching it.(?)

"tool goes this way"...just the drill partb of the operation.
the angle cut with the tool (boring tool) going at needed angle.

Running production good to make or buy a special that would finish the bore after a flat bottom was made to almost depth. Grind down a 9/16 reamer to the .282 bore, and make it end cutting to clean up and size.

Needing a special call Special Drill and Reamer in Troy Michigan. I don't know what specials cost nowadays.
 
Qty (1) line was all that was needed to be added.

A "Centerline"

Please try to speak the language of the machinist when making a "drawing".

"Paint" the 21st century's digital answer to "finger paint for the kinders", while eliminating any/all "Cleanup".
 








 
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