Sharpening slotting bit

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Metalman
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Sharpening slotting bit

Post by Metalman »

I have a project that requires me to broach round holes to square in some bronze door hardware. The plan is to use the Bridgeport slotting unit. I have no tooling for it never used it. So after some google searching I ordered some 3/16 high speed steel and made a tool holder from some 1144.
Looks like I'll have to advance the tool into each corner one at a time until the desired size square is reached. The round holes already exist.
I'm looking for suggestions on how to best sharpen the business end of the tool bit. Only thing I thought of doing so far is to center it in a 4-jaw on the lathe and figure out a way to grind the end concave and hopefully have 4 cutting corners. Any thoughts on this definitely welcome.

Photos of the tool with the raw tool steel installed:
Attachments
slot-bit-holder.jpg
slot-bit2.jpg
Ernie F.
John Evans
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Re: Sharpening slotting bit

Post by John Evans »

How about using a center drill or spotting drill in the lathe ,that should generate the edges needed.
www.chaski.com
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BadDog
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Re: Sharpening slotting bit

Post by BadDog »

I would guess the bit would be HSS, so not something my spotting drills could handle, maybe carbide? And I think the edges would be too delicate as well. I've only played with mine a bit when I got it, mostly making sure it was in good working order, but the bit I made took a fair bit of a beating. You have to be very careful of your in feed, particularly with the length of stroke indicated by that hang out pictured. My playing around bit had only 2 cutting corners and looked a lot like an unground blank. You also have to build clearance into the holder, or grind it into the bit. And for the length shown, both could be problematic, and likely only grinding is realistic (assuming the hole size dictated the long spindly bit hanging out like that?). Anyway, the slotter does work rather well and as expected, and I'm sure that real world experience would expose a lot more over time that I didn't take. Mine didn't like much in-feed at all, but that could just be my bit grind choices.

Anyway, I don't know if it's realistic to try to get 4 cutting corners on that bit. You do was some positive rake, so 2 corners made more sense to me, but that does limit your in-feed to only one axis. In practice, it might be best to go with one corner allowing in-feed on both axis, with appropriate clearance of course.
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Re: Sharpening slotting bit

Post by spro »

Since I have an E head project and wondered about the same thing, I splurged on an actual Bridgeport .250 slotter bit. First, they are one piece with a shank like an end mill. From there, the .625 is ground after the ram to .220 minor and .471 major of this rectangular section. Total length is 2.90 and only about .430 is cutting/ ground surface.
The main thing is they are centered and broader in support. The grinding appears central of few degrees and just enough to present that angle among 4 corners. The other thing about the .430 area, it is tapered very slightly at the slot linear sides. Another precise grinding for relief.
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BadDog
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Re: Sharpening slotting bit

Post by BadDog »

I've looked off and on for some original bits, but they always cost more than I can justify. But the pics are quite useful for understanding how they can be managed. This search produces a few examples among the matches. Seems like best bet to get results is searching for "shaper" rather than "slotter" or the like.

I also bought some of the inexpensive boring bars that take HSS bits at each end. 5/8" diameter, cut them in 2, and you've got a pair of bit holders for larger bores at least.

And is the full set, if you can afford it. But at least good for ideas and better understanding.
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SteveM
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Re: Sharpening slotting bit

Post by SteveM »

Could you use a rotary broaching bit? It would have sharp corners and relief ground into it.

You would be using it one corner at a time, I suspect, not trying to broach the hole in one shot.

Image

You would present the tool to the work straight and not wobbling, as they are normally used.

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SteveM
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Re: Sharpening slotting bit

Post by SteveM »

SteveM wrote:Could you use a rotary broaching bit? It would have sharp corners and relief ground into it.

You would be using it one corner at a time, I suspect, not trying to broach the hole in one shot.

Image

You would present the tool to the work straight and not wobbling, as they are normally used.

Our own Frank Ford made his own:
Image

Here's how he did it:
http://www.frets.com/HomeShopTech/Tooli ... aking.html

Steve
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Metalman
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Re: Sharpening slotting bit

Post by Metalman »

The bit in the holder is HSS, I don't think my HHS drills would work. The length is the tool material as I bought it, yes too long. I need about 1" sticking out of the holder on the finished tool, In the photo it's sticking out 1.75".
Russ, are you saying I'll need some relief ground in above the cutting edge? I could get it done working with one tool corner, that would make grinding the tool easier.
I guess I was looking to leave the part clamped and move the tool in four directions, but I can rotate the vice.
I found the same photos on ebay that's where I got the design for the tool holder.
Ernie F.
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Metalman
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Re: Sharpening slotting bit

Post by Metalman »

Thanks Steve. What Frank did to concave his broach is pretty much what I was thinking. But in reality hand grinding and going one corner at a time would likely work OK. I wouldn't mind having one of those rotary broach systems but it seems the good ready made ones a expensive and I don't have justification to buy one, (yet) :) .
Ernie F.
earlgo
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Re: Sharpening slotting bit

Post by earlgo »

A gentleman by the name of Walter B. Mueller wrote a book "Building a Single-Shot, Falling-Block Rifle Action" published by Village Press Publications, Traverse City, MI. ISBN 0-941653-54-4.
In it are instructions and drawings on building a clapper-type shaping tool for the Bridgeport Quill. I could imagine this working for scraping the corners out of a round hole with the proper tooling.
I got my copy from Brownell's in Montezuma IA. Current price is $20
http://www.brownells.com/gunsmith-tools ... 13833.aspx
It may give you some ideas. I'd copy and post the information but I think that it would infringe some copywrite law or other.

--earlgo
Before you do anything, you must do something else first. - Washington's principle.
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BadDog
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Re: Sharpening slotting bit

Post by BadDog »

Metalman wrote:Russ, are you saying I'll need some relief ground in above the cutting edge? I could get it done working with one tool corner, that would make grinding the tool easier.
I guess I was looking to leave the part clamped and move the tool in four directions, but I can rotate the vice.
I found the same photos on ebay that's where I got the design for the tool holder.
Yes. Any cutting tool will benefit from at least a small amount of clearance/relief behind the cutting edge. This is most important (and required) for "feed" tooling such as a lathe tool, fly cutter, etc where you feed into the work while cutting the work. If you do a slot-step, so that you make the cut without any sideways traversal, you can get away less clearance, and may help with long slot tooling with a long bit that wants to deflect and chatter. But that means you can't crank advance as it's running, and generally would be realistic only for something like a manually operated slotter (like the ones you see on lathe beds actuated by hand with a lever). Single stroking then stepping with the E-Head would be less than ideal.

Regarding 4 direction, this would be a good case for some sort of indexing. If the part doesn't naturally index, something like the 5C blocks would be good. I've seen vises mounted on machined blocks that then mount in another vise. The top vise then indexes using the jaws of the bottom vise. The "screw-less" or "grinding" type vises work well in this capacity by using their precision surfaces for 4 side indexing. And so on. Rotary table or indexer is another option.
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Re: Sharpening slotting bit

Post by spro »

Looking at the link;, MetalMan built a #10 and I was describing a #3. Looking at the side view of a #3 , you can see the slight taper of the slotting faces. I needed to actually see how they did that. There is .007" taper over .425" length of one side. Not much but required.
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