View Full Version : Milled slot problem

09-05-2006, 07:31 PM
Ok guys, I need some ideas. I need to mill a 3/16" slot in aluminum. That in itself is not a problem but one side needs to be dovetailed 60*. The base of the slot is about 1/4". The smallest dovetail cutter I've found is 3/8" diameter.

???? Make my own or regrind a 3/8?

09-05-2006, 07:41 PM
That's only alum., hell I'd just use a wood chisel and a BFH!

09-05-2006, 07:42 PM
He's had a half-pint, ignore him and wait for a sober answer!

09-05-2006, 07:45 PM
{wait for a sober answer!} Damn, didn't know you could get a sober answer on this forum.

09-05-2006, 07:46 PM
good evening, Ken.

have you tried Brownell's? they have some pretty small dovetail cutters. i cannot find my catalog at the moment, but they have a web site. www.brownells.com [i think]

that is a pretty small one. good luck.

if i couldn't find a cutter, i think i would grind a single point tool and do it that way. if you have a shaper, it would be easy if it is as i visualize it.

free advice. worth exactly what you paid for it, but probably overpriced at that.


09-05-2006, 07:47 PM
EVERYTHING is relative!

J Tiers
09-05-2006, 08:21 PM
How about setting it up at an angle, either the head, or the piece?

Lots cheaper than a new cutter...................

09-05-2006, 08:26 PM
Dang power has been out here for the last half hour so I hit the bottle too. :D

While the pc was down, I ran out and took some measurements. It appears that the slot is smaller than I remembered. Here's what I need to cut on the radial face of a disk--Three slots. (No shaper)

Thanks Bill, I'll have a look there.


J Tiers
09-05-2006, 08:33 PM
OK, a BLIND slot........... that obviously changes things.......

Looks like you DO need a dovetail cutter. Annd. yes Brownells has some little ones for sight dovetails.

John Stevenson
09-05-2006, 08:36 PM
If it's in aluminium then make a D bit up.


09-05-2006, 08:38 PM
Well, I just checked Brownell's. The smallest is .245 x 60*. :(

I've got some leeway (+.003) on the dimensions but not enough to use that cutter.

09-05-2006, 08:49 PM
If it's in aluminium then make a D bit up.

There you go! Thanks John! See there, all it took was a master. ;)

I was kinda figuring I'd have to make a cutter.

09-05-2006, 09:49 PM
I'd agree with the single flute. You can make the major diameter whatever it needs to be. But it would have to be a modified D-bit I should think. The D-bit cuts on the end and that's where the clearance is ground. If this is used as a milling cutter it will have to have side clearance in order to cut. IIRC the single point tools used for engraving on pantograph mills would be a good example. They're ground off center to provide the clearance.

I think this means that you could start with a blank, drill a cross hole at some convenient point so you can keep track of orientation, then chuck it in the four jaw or use shims adjacent to what will be the final cutting edge. Then when you turn the dovetail angle and cut the flat to form the cutting edge you will wind up with the cutting edge proud of the remainder of the profile.


Ian B
09-06-2006, 12:54 AM

I don't know what the application is, how long the slot needs to be or if it's a through or blind slot. But as it's a pretty small cross section in a soft material, could you make up a broach of that shape? Or make a small planing tool and use the mill's vertical feed to push it through?


09-06-2006, 01:15 AM
I'm with Ian. You only have a very small amount of material to remove from the slot on one side. A simple ground form tool pushed through the slot a few times will work perfectly. Take off a few thou each time. I do this all the time on my lathe.

Allan Waterfall
09-06-2006, 03:06 AM
Is it a job where you could mill a wider slot and then counter bore and bolt a separate piece from the top like a gib.


Norman Atkinson
09-06-2006, 03:13 AM
Isn't there still this mental blockage about end mills and slot drills?
An orthodox end mill will not cut an accurately dimensioned slot but a decent slot drill will. Then, and only then does the dovetail cutter be introduced and then it only cuts on one of its two edges at a time.

Or at least, that is the way that I was taught.


09-06-2006, 03:38 AM
Norm we must have attended the same school of thought. I bet you are still hand grinding your endmills, too. I can't see so good now, but I still touch them up by hand, extends their life greatly.

Norman Atkinson
09-06-2006, 03:47 AM
Hooray, Hooray!

And I thought that I was sitting on a rock by myself and throwing snowballs at the moon!

Friend, Friend!


Note the cleaned up version- part Biblical and part Puritan and part Ancient Greek.

The ancient one was in the 'nuddy'

09-06-2006, 03:57 AM
Ya know, I was tested yrs. ago for a screw machine shop. The supervisor handed me drillbits to sharpen by eye, no guages. He gave me about 2 min., and got hired. Had to learn real fast. Some of those bits cut within .001, which made him very happy!

09-06-2006, 08:18 AM
Isn't there still this mental blockage about end mills and slot drills?
An orthodox end mill will not cut an accurately dimensioned slot but a decent slot drill will. Then, and only then does the dovetail cutter be introduced and then it only cuts on one of its two edges at a time.

Or at least, that is the way that I was taught.


There is no difference between what is called an end mill in the US and a slot drill in the UK. They are basically two flute end mills.

This was discussed a year ago, and put to rest.


J Tiers
09-06-2006, 01:09 PM
Well, they are "center cutting" end mills. While most 2 flute ARE, and most 4flute are NOT, even that isn't a rule.

Plus, I don't believe that ANY end mill cuts a perfect slot, any more than a drill drills "on-size"..... I'd always cut with an undersize EM just because.

if you want a one-pass slot, do it on your horizontal mill.

Norman Atkinson
09-06-2006, 01:23 PM
East is East and whatever.
I apologise for flogging the issue but we live in world which grows by the day.
If I recall, Jim and J that we had query about electric plugs in Europe and despite photographic evidence there was still wide variation in practice.

What appears to be the case is that it may be necessary to make one's own cutters- and you guess is as good as mine what will be copied. If it is on the dovetail cutter, it becomes an "end mill" UK variety rather than a US drill and might over cut.

I therefore agree and disagree!
However,I do send my kindest regards without evasion or equivocation!


J Tiers
09-06-2006, 05:12 PM
If I recall, Jim and J that we had query about electric plugs in Europe and despite photographic evidence there was still wide variation in practice.

Say what, bubba?

I am SO not plugged into that.

09-06-2006, 06:07 PM
Ken... another idea would be to use a Inverted coned carbide burr. They come in 1/4" size. That might work for you or just a coned bur and set the work to the right angle this would give you a the needed taper. Unless your set on making a bit.

Norman Atkinson
09-06-2006, 06:10 PM

It always looks fine on paper when something is put down in black and white. It suggests that there are no shades of grey/gray. I've lived too long to trust the so called experts. I live in Menorca for part of my year. One would reasonably expect that the voltage to be 220AC but the next village is 110v and the plugs are two different sizes in my house and a set of unearthed ones making three varieties. The plumbing and one would expect it to be metric- but it is Imperial but my house in England is Metric. So, I buy my taps and dies in Spain for my Imperial gear here.
In a few hours, I will be buying Euros from pounds sterling- a new car, topping up the bank accounts etc. So I can write a Eurocheque as I have a house in France as well as in Spain and credit my French account. You must be joking, it doesn't work like that. You would expect that as it is all Europe that I could pass from one country to another without being stopped but I can't. I can go from France to Italy for an ice cream and from Germany into Austria but I get stopped on many other frontiers. I have to have a Spanish Identity card but one isn't needed in the UK for Spanish nationals.

Believe me, I can cope but I simply view the World with the reserve and caution it merits. I act within the confines of regarding life as a lottery.
So what have a few odd milling cutters in Imperial or Metric or both and whether they have 1,2 3 or 4 teeth matter.

Others, JT, may have problems but then you will notice that the Forum is full of such creatures!

Yes and No?


09-06-2006, 06:15 PM
Denmark still has border guards the last time I was there and they refuse to give up the Danish Crown as well. They won't take down the guards because the border is with Germany and they still remember. They are happy to take the money of the german tourists but there is a standing joke my cousin told me:

Why do all the German tourists have bicycles on the roofs of their cars?

Because, last time they had to walk home.

09-06-2006, 06:47 PM
Norman, I thought that this post was related to a question about how to cut a little dovetail. If Ken told us whether it is a through slot or one ended slot it would have helped. I would take a slot saw and cut the dovetail slot wall, then enlarge it with the end mill. To make it right dimmension I would make more than one pass if necessary.

Norman, this is absolutely impressive, you just knocked my socks off, two houses abroad and perhaps you have even one (more? do not hold out on us now!) in the UK, what about the US?. And, how many Mercs? I gather they are at least the top of the line. Do you get one on the way to Spain, and then another one on the way to France? And, you will be writing cheks on a French bank? How retro. I do not know how old you are, but you are going fast, downhill that is. You are on a wrong BBs with all that bull. What did you do? Married B. Gates's flower girl? But, as they say, the older we are the better we were. Moderation/modesty is a good thing, mother used to say. Vic Smagovic

09-06-2006, 07:01 PM
I am slightly curious Norman. Without giving anything much away which is address #1?


09-06-2006, 08:38 PM
I have an assortment of 110 & 220 volt plugs, mostly Hubble. They are twist-lock and straight.

I have been trying all afternoon, and for the life of me I cannot find one that will mill an acceptable dovetail.

09-06-2006, 10:17 PM
I had to finish another reamer first and get a starter put together but I got a chance to do a little work on the face cutter today. All that's left is to cut the dovetail. I made a D-style cutter and I'll cut the dovetail in the morning.

Here's the face cutter so far. The three carbide bits in front will be held in place with a screw and sleeve. I may have to reduce the diameter down to the taper but it looks like it'll work.


Here's the reamer I was working on too. Grinding final diameter.


09-06-2006, 10:22 PM
Here's the reamer in action!


Norman Atkinson
09-07-2006, 02:30 AM
Vic and Evan,
The phone rang last night. Long time since it did from my old aircraft engine fitter but we go back- would you believe- to the 12th Sept 1948. Johnnie was the young lad who joined up in the Royal Air Force with me, had 6 or so weeks training and I trusted my life to him. Well, I might have and he was badly injured when a drunken pilot fired a Spitfire up with the throttle gate full open. Johnnie has now a War Pension, it was my turn!
He was in a series of disasters but he is now financially secure for the rest of his life. We had a fit of irreverent giggles last night- I had cut a way through all the British red tape and officialdom. I was doing precisely what I had trained for. As he puts it, Atkinson, the Bastard! Vic, the secret is never to forget those who you needed in the past. I still have that precious thing called Life. Others died, I lived.Thanks Johnnie- we will march as best we can amongst our brothers- there are so few of us left!

It all breeds determination. Whether my wife and I are sort of comfortably off is really immaterial. What we have is from sheer hard work. You can do anything you want if you can 'live on cabbage and cheese sauce' to ride out the storm. Answering Evan's query. it is the bungalow. However, it is important not to look at where I live but to see that hundreds of others are living in exactly the same way as us. If you were to look closely, there are posher houses than ours. Again, do you realise that one in five people in the UK have second homes- or better? Again, I don't feel unusual or different to my fellows. It is important to mention that Britain plc is not the Britain of two
half starved airmen who had faced the starvation of a 6 year war. Both of us had been bombed repeatedly, we had and still live with a bit of surprise and relief that we have lived- to see another day.

Is that an answer? Evan knows that only in the past few months that my wife and I were targetted by animal rights activists. We lived in peril of our lives. We had invested what little money into a drug firm which was actively researching how to give hope and life to both animal and human.

Today, Vic, our Evan is putting his trust in those drugs which might cure his deafness.Yes, we paid for that and I hope that it was money well spent.
It is going to a friend- and I hope that it works.

But Vic, for Johnnie and I, we will never have the chance that Evan has.
Johnnie, my 'brother' and I never and will never have that chance. We will remain deaf- till death us do part.