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asallwey
04-30-2015, 10:12 AM
I have a very basic question about dovetail cutters, I currently have none. I've noticed that build articles usually specify the width of cutter. 3/4" is a common recommendation for things like toolholders, sometimes larger.

So, How does the cutting height change as the width changes?

Catalogs don't seem to provide this info. A HSS cutters search on MSC gave the following info on the first item in the list.

Brand:Interstate, Price: \$30.30 ea.
Included Angle ( ) 60
Cutting Diameter (Inch) 3/8
Cutting Diameter (Decimal Inch) 0.3750
Cutting Width (Inch) 3/16
Cutting Width (Decimal Inch) 0.1875
Material High Speed Steel
Shank Diameter (Inch) 3/8
Overall Length (Inch) 2-1/8

My MH 25th Ed. gives a 5/16" height for 3/4" & 9/16" for 1 3/8", and 2 larger cutters, but no formulas. Ok, so they cut higher as the cutter gets wider. Is there a rule-of-thumb that can be used to select the appropriate height when buying? I've also noticed the price can get steep when the diameter goes beyond 3/4".

I applied a little math and for the 3/4" cutter I get value of 0.3248 whereas MH says 0.3125. Must be a factor I'm missing? Just seems this would be a good thing to know, regardless the size of the project. I can see wanting to make items smaller than toolholders where a 3/4" would not work.

TGTool
04-30-2015, 11:32 AM
By cutting height I presume you mean the vertical height of the dovetail that a particular tool will cut. There's probably not an absolute relation because it will depend on how the cutting edges are merged to the tool shank. In theory, you'd subtract shank diameter from cutter diameter and divide by 2. This will give you the horizontal width and you can calculate height from the trig relationship Tan(angle) x width to get the opposite side. Tan = opp/base. In real life the shank may be necked down a little to give more height, or the cutter might be truncated.

With the specs you give for that Interstate cutter you can see that the cutting diameter listed is the same as the shank diameter, 3/8". Since the cutter diameter is 3/8", we know it will cut a slot this wide at the inside corners so when they list "Cutting Width" as 3/16 that must mean something else. Further, that 3/16" cutting width can't be the undercut distance since the whole cutter is only 3/8" wide and that would mean a shank of 0" diameter. So in this case I think they're telling you that it will cut a 3/16" high vertical wall and we could then back calculate how thin the shank must be at the neck to allow that.

asallwey
04-30-2015, 12:44 PM
Yes I mean the vertical height. I did the math you mentioned and my height/vertical result was a little higher than MH (in #1). I'm just a rookie at this and when I read the last article for some reason this question on dovetails sprang to mind. I appreciate your comments.

garyhlucas
04-30-2015, 01:39 PM
I think the difference is because the dovetail cutter probably doesn't have a completely sharp corner on the flutes, which would break easily.

Paul Alciatore
04-30-2015, 06:35 PM
I looked up the cutter you are talking about.

http://www.mscdirect.com/browse/tn/Milling/Dovetail-Cutters?searchterm=milling+cutter+dovetail&navid=4287923893

The numbers given here are not sufficient to determine the height of the dovetail that it can cut. The shank diameter is misleading if you are not looking at the cutter itself or a photo of it. They are referring to the part of the shank where your collet or mill holder would grip it. But, the shank between that 3/8" diameter and the cutting section is a lot smaller, probably 1/4" or less. But that is not specified.

The "detailed" description is not of any more help as it just gives the same information. A total waste of an internet page.

I do suspect the outside edge of the cutter is a sharp vee or at least intended to be so. But there is no way to know for sure what the height will be unless you have one in hand. Of course, it may be some kind of standard size so everybody knows. Therefore we don't really have to publish them. Grrrrrrrrr!!!!!

Here is one that is specified a bit better.

http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=367-0140&PMPXNO=945939

Yours is probably similar. But who knows for sure?

You could try calling Interstate. Their web site is not very helpful. Perhaps they will send a paper catalog.

http://itctoolcorp.com/Products.php

asallwey
04-30-2015, 06:57 PM
Paul,

My only interest in the cutter I listed was that it was the first one to come up and I was showing the extent of catalog information. Again, I have no experience with dovetail cutters. My question arose from curiosity. There always seems to be a readily available formula for calculating most anything in machining. Looking at the catalog listings it seems just like any given size cutter looks the same in any brand, and the stated dimensions usually are the same.

I'm just curious!

38_Cal
04-30-2015, 07:03 PM
With the Enco cutter used as an example by Paul, the "cut width" dimension would normally equate to the approximate depth of the cut to get a full profile dovetail with sharp points at the top of the cut...assuming that a minimum diameter cutter was used to rough out a slot first. That's my story and I'm stickin' to it!

TGTool
04-30-2015, 07:12 PM
Here is one that is specified a bit better.

http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=367-0140&PMPXNO=945939

Yours is probably similar. But who knows for sure?

You could try calling Interstate. Their web site is not very helpful. Perhaps they will send a paper catalog.

http://itctoolcorp.com/Products.php

Paul, it appears to me that the Enco listing gives exactly the same data that Asallwey posted so it doesn't add much to our store of knowledge. The photo does show the reduced diameter shank. Again, the 3/16" is what I think they're trying to tell us about vertical height, though I wouldn't bet serious money on an exact dimension sight unseen.

Paul Alciatore
04-30-2015, 07:35 PM
I understood that and I answered it with another example. My point is

THE MSC WEB PAGE DOES NOT HAVE ENOUGH INFORMATION TO ANSWER YOUR QUESTION.

And the Enco page does because it adds the 3/16" cut width spec. So, the Enco page is better, at least for this item.

You didn't miss anything. It just wasn't there. Poor salesmanship, IMHO.

I guess the lesson is, use a supplier who provides the information you need.

Reminds me of the old joke. A local was asked for directions to a location across town by a visitor. He started to answer three or four times, always with different, partial directions. But could never complete them. So he finally said, in frustration, "Well, I guess you just can't get there from here."

Paul,

My only interest in the cutter I listed was that it was the first one to come up and I was showing the extent of catalog information. Again, I have no experience with dovetail cutters. My question arose from curiosity. There always seems to be a readily available formula for calculating most anything in machining. Looking at the catalog listings it seems just like any given size cutter looks the same in any brand, and the stated dimensions usually are the same.

I'm just curious!

Paul Alciatore
04-30-2015, 07:41 PM
Well, that 3/16" certainly does sound like what Asallwey was asking about. But how exact it is I do not know. I would say that both MSC and Enco could do a better job of describing this tool and probably all the other similar ones.

Frankly, I do not know a lot about these cutters and if I was designing a dovetail, I would try to have the cutter on hand BEFORE I made that design final. I have made a few and that's the way it happened, weather by design or by accident I won't say. If I was in doubt, I may even buy two or three to be sure. But that's me. Your mileage (and pocketbook) may vary.

Paul, it appears to me that the Enco listing gives exactly the same data that Asallwey posted so it doesn't add much to our store of knowledge. The photo does show the reduced diameter shank. Again, the 3/16" is what I think they're trying to tell us about vertical height, though I wouldn't bet serious money on an exact dimension sight unseen.

TGTool
04-30-2015, 10:41 PM
I understood that and I answered it with another example. My point is

THE MSC WEB PAGE DOES NOT HAVE ENOUGH INFORMATION TO ANSWER YOUR QUESTION.

And the Enco page does because it adds the 3/16" cut width spec. So, the Enco page is better, at least for this item.

You didn't miss anything. It just wasn't there. Poor salesmanship, IMHO.

Well, I'll have to admit that I'm just lost in the woods then. Both MSC and Enco list a "cut width" or "cutting width" in addition to cutting diameter so are providing just the same information. That is, I'm assuming that they're not just calling cut width one half of cutting diameter since that would be self evident and redundant. Not that irrelevance or redundancy would necessarily be important for the catalog entry. They give dimensions in both fractional and decimal numbers which is maybe a sly comment on their opinion of the intelligence and education of their customers. :D

I can say from experience that some of those numbers are inexact. I did a job once using a 1-3/8" dovetail cutter and assumed that was 1.375". Yeah, dumb assumption without actually measuring. It was actually a few thousandths oversize so I had to do that job over and actually measure the dovetail size as it progressed to be sure it came out right.

Paul Alciatore
05-01-2015, 01:52 AM
I'm sorry, I did not see the cutting width on the MSC page. Humble apologies.

Are you really sure it was there all along? I really didn't see it before.

Ryobiguy
05-01-2015, 02:30 AM
I have a 3/8" dovetail that I probably got from Enco. Max dovetail cut height/depth seems to be right at .200". Thinnest diameter between shank and cutting flutes is .160".

TGTool
05-01-2015, 08:49 AM
I'm sorry, I did not see the cutting width on the MSC page. Humble apologies.

Are you really sure it was there all along? I really didn't see it before.

No, I put it on the MSC page after you posted your comments just to mess with your head. :) If I'd never missed something obvious I could be self righteous about this but I'm in the same boat lots of other places.

asallwey
05-01-2015, 10:31 AM
I guess I raised an interesting question!

Just seems like there would be cutter manufacturing standards that come into play or every mfg. would be saying their cutters are better because they are cut higher or lower. I would have thought someone here would have raised this question before.

Alex

TGTool
05-01-2015, 12:47 PM
Well, it's not like Woodruff keys where there are standards for key diameter and thickness and then corresponding standards for height of the key above the shaft, etc. The cutters for those then need to adhere to a diameter and width. Which in turn means that they're not re-sharpenable since that would change the size one way or another.

Dovetails might be any number of widths and heights, width constraints might require a particular cutter diameter, and machine availability might require a particular shank size. Manufacturers of cutters might have similar design opinions about whether their cutters would do maximum height and thus compromise shank neck diameter, or would have maximum rigidity and strength with a compromise on cutting height. You just can't have everything. It's a little like the price-speed-quality dilemma. You can never get all of everything so you choose some priorities and live with it.

So, you check out the various tools offered and get the one that most nearly fits your needs. Or you go back to the drawing board. For instance, if the cutter won't cut the necessary height you can reduce the height, or enlarge the slot in the middle putting flats on the sharp corners and/or a similar change for the male side. They're all choices, just like which horizontal surface you choose for a mating surface and which gets the clearance. Usually you'd want the widest contact for rigidity but there could be other considerations.

Paul Alciatore
05-01-2015, 02:34 PM
Yes, when designing and cutting a dovetail, the limitations of the cutter must be kept in mind. I believe this is what the OP is doing or at least starting to do.

asallwey
05-01-2015, 08:55 PM
Right you are Paul, I do want to undertake a project with a dovetail. Never having used such a cutter I had sizing concerns and thought I would explore them here. I guess the key is to "measure twice and cut once" and it should work out. Thanks guys!

oldtiffie
05-01-2015, 09:04 PM
Hopefully having sorted out the dimensional details of nominal/actual sized dove-tail cutters it is safe to get on with the process of cutting the dove-tail(s) - which can be either male or female.

Actually using (hopefully) precision rollers and/or balls (for actually measuring the cut dove-tails) wit the selected/designated cutters/ it is time to actually cut the dove-tail - keeping in mind that the reduced cutter diameter (for the dove-tail) on the cutter is or may be quite fragile and needs to be treated accordingly.

The common (and cheaper) dove-tail cutters are "straight toothed" and more likely to break or "chatter" whereas the "spiral" cutting edged cutters are far superior - and more expensive.

And now for some:

Shop Maths 101

Shop Geometry 101

Shop Trigonometry 101

http://www.webmachinist.net/dovetailcalculating.html