milling slot question

I've got a little job I need to do/get done. I am working on the wing strut fittings for the bush-plane. There are 4 struts - so 8 strut end
fittings. They are made of 1X1 6061T6 - 4 abot 4 1/4 inches long, and 4 about 5 1/2 inches long. 2 need 1/4 inch slots, 4 need .195" slots, and 2 need 3/16 " slots - all 1 3/8" deep.
I may have the use of a bridgeport style mill that used 3/8" shank cutters, and I have located a 3/16" end mill that has 5/8" cutting depth (end mill)
How close to 3/16 will I likely be able to get? (thinking the cutter is going to want to "walk" a bit in the cut) Would it help a lot if I drilled a row of 1/8" or 5/32 holes down the center of the slot first to reduce the chip load????
Or do I just farm it out to a CNC shop??
If I had access to a horizontal mill it would make life a lot easier, but nobody has them any more.
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snipped-for-privacy@snyder.on.ca fired this volley in

How do you figure to get a 1-3/8" deep slot from a cutter that only has a 5/8" cutting depth?
If you take the cuts in shallow increments, AND you don't have any play in your spindle, you should be able to get within a half-thou. of the cutter diameter, or so.
But not that depth!
L
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On Sat, 16 Jan 2016 10:03:28 -0600, "Lloyd E. Sponenburgh"

Lay the 1X1 in the vise, with the desired slot vertical. Mill the slot from the end to the stop-hole. Keep milling bit by bit 'till you reasch full 5/8" depth for the full 1 3/8" length of the slot. Release the vise and flip part end to end, reclamp and repeat, cutting from the other end, untill the depth of cut excedes 3/8" and there is no more metal in the slot.
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A dumont push broach will also work. Been there done it. Still use the jig for some slotting jobs.
Best Regards Tom.
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wrote:

Pretty difficuld to do with a shaper to get a clean cut at the base of the cut (end of the slot) unless cutting across the stock (1 inch cut) and then to cut 3/16" wide and 1 3/6" deep would be some fun - - - -
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snipped-for-privacy@snyder.on.ca fired this volley in

It's pretty difficult to get a clean, well-matched cut when you have to flip the work and cut a 'half-slot' on each side, too.
If you don't have the capability to cut a slot that deep, likely you don't have the tools or experience to get the work perfectly-registered on the flip, either.
Besides, cutting two 'features' on opposite sides of a piece of stock so they meet in the middle is NOT "milling a slot". It's exactly what I just described in the prior sentence.
Rule of thumb -- if you don't have the tools or ability, then farm it out to someone who does!
I'm not an 'experimental' pilot, but I am a pilot. I know somthing about how planes are put together (yeah, even the structural parts, having helped A&Ps over many hundreds of hours, just so I'd learn something). I seriously doubt that a mating feature like that need be as accurate as you're demanding in order to be robust and safe. If play is problem, mill the parts for a too-tight fit, and adjust for perfection with hand tools.
Lloyd
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On Saturday, January 16, 2016 at 10:20:20 AM UTC-5, Clare wrote:

I think I would do it on a table saw. You could try making one out of wood and see how accurate you can make the slots.
Wear eye protection
Dan
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On Sat, 16 Jan 2016 10:01:04 -0800 (PST), " snipped-for-privacy@krl.org"

The fun comes in holding the piece in place verticaly, cutting the slot 1 3/8" deep into the end of the workpiece while dodging all the flying hot and sharp chips, and getting an acceptable finish AND accurate slot width.. This needs to be "aircraft precision", not " lay it out with a crayon and cut with an axe" These 8 pieces keep the wing from folding up in flight, or falling to the ground on landing.
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wrote:

That is done by the drilled "stop hole" - or by the end mill finishing the slot - 3/16" slot with 3/32 radius.
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On Sat, 16 Jan 2016 13:37:21 -0500, "Jim Wilkins"

The cutter would have to be at leadt 2 3/4" plus the diameter of the arbor to do the job. Unlike an end mill, you can't cut to a straight end cutting through the 1 inch dimension, and you can't flip it over to cut from the other end.
I thought about trying to jig the parts up to slit the ends with the 14 inch cutoff saw (abrasive wheel) but the thought of loading the wheel with aluminum changed my mind on that pretty quick - not to mention the flexability of the fiber abrasive wheel..
A "cold cut" saw would work - it turns a bit slower than the average table saw, and the blade is made for cutting metal - but I don't have one and the quality of the finish of the cut would likely leave something to be desired.
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On Sat, 16 Jan 2016 14:22:09 -0500, snipped-for-privacy@snyder.on.ca wrote:

Cold saws are cutoff saws. With a few exceptions (Amada makes one such) they don't leave a great finish.
What you want, I think, is someone equipped with a horizontal mill who does a lot of slotting work. As for the geometry, shank-type cutters for a vertical mill can cut slots, but I've never seen one that could handle that depth. Arbor-type slotting mills are the tools that would give you the accuracy and finish you're talking about, and they're mostly horizontal-mill tools. They come in a wide range of diameters.
I'm speaking not as one who has done it, but who has seen thousands of milling cutters and tool setups -- run by other people. d8-)
--
Ed Huntress

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On Saturday, January 16, 2016 at 2:22:00 PM UTC-5, Clare wrote:

You have a solution with your friend doing it. But do not knock using a ta ble saw with carbide tipped teeth for cutting aluminium until you have trie d it. It is noisy, but quick. And the finish is not bad. Try searching o n " cutting aluminium table saw ". You will get a couple of pages of links to that topic.
Dan
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On Sat, 16 Jan 2016 17:07:12 -0800 (PST), " snipped-for-privacy@krl.org"

I've done it several times. I had a 10 inch "Beaver" table saw and used it to cut 2 inch blocks of aluminum for the engine mounts.(sold the table saw almost 10 years ago - did I mention we are 16 years into this build???) The whole garage was full of sharp shiny chips of aluminum.
I also cut some 3/16" aluminum plate for an engine cover - and that cost me over $100 for a new armature for my favorite circular saw -and spread chips all over the back yard. THAT cut was extremely noizy-.
The cuts were smoother than chopping with an axe, but would require a lot of sanding or grinding to make the surface quality I want for these parts - which would make any kind of accuracy very difficult.
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On Saturday, January 16, 2016 at 8:28:02 PM UTC-5, Clare wrote:

I would not recommend a circular saw for aluminium. But do use a table saw whenever it seems like the best way that I have. I have some sheet metal to keep sawdust out of the motor and it works for aluminium chips too. Th e aluminium chips are a big pain.
If you do not have any aluminium files, I would recommend getting one. The Type A is the best in my opinion. I have a bunch of files from Boeing Sur plus, but they do not work as well for good finishes as the Type A I bought many years ago.
Dan
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On Sat, 16 Jan 2016 20:28:11 -0500, snipped-for-privacy@snyder.on.ca wrote:

Not that it is particularly relevant in this application, my favorite tool for cutting aluminium is my cheap ass band saw ("Simple Simon" brand from Wilson Brass and Aluminium Foundry in Toronto) with a 4TPI wood blade. This saw doesn't even come with a rip fence but modifications have been made.
--

Gerry :-)}
London,Canada
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On Sat, 16 Jan 2016 10:20:28 -0500, snipped-for-privacy@snyder.on.ca wrote:

I'm going to assume the slot depth is 3/8", not 1-3/8". While the 3/16 end mill may cut close to .188, as measured with a block or pin, unless you have flood coolant with plenty of velocity available (unlikely on an un-enclosed mill) the sides of the slot will be quite rough. I'd use a 5/32 2-flute cutter. Bring the slot to within .010 of depth with a couple passes with the cutter on center line. Widen the slot by offsetting the cutter about .005 per side and measure the result. Set your final offsets taking into account the result of the previous cut and bring the slot to final depth at the same time. You can climb mill the final passes if you find you get a better finish that way. Brush on some alum-tap or kero or WD40 before each pass.
Don't bother with the drilled holes unless the slots have blind ends. If they do, a hole to depth at each end gives the end mill a place to dwell at the ends without rubbing, and acts as a visual cue.
Not knowing the condition of the mill it's hard to predict how close you'll get, but with a bit of care I'd expect to get within 3-5 tenths on my DRO equipped pretty-tight mill. Within a few thousandths without paying a lot of attention.
--
Ned Simmons

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wrote:

The slot depth is the full 1 inch thickness of the stock, and the length of the slot is 1 3/8" The mill doesn't have a DRO. It is old but lightly used and well maintained. Being a 3/8" mill holder, it is almost impossible to buy an end-mill smaller than 3/16 with a length of 1/2" or more, which is required to cut the full slot, cutting from both sides. Our local machine tool supplier doesn't carry them, but an old machinist friend has a 5/8" long cutter from a box of cutters he bought at a close-out auction over 10 years ago - brand new never been used, that he has given me.
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    [ ... ]

    O.K. Slots cut across the end and 1-3/8" from the end of the workpiece to the end of the slot.

    There is a reason for short lengths with small diameters. They tend to break easily when longer.
    Now -- you say it is a "Bridgeport type" mill -- and never say that it is truly a Bridgeport, so I may interpret that as meaning a vertical spindle mill of unknown size. If it is truly a Bridgeport, or a clone of the Bridgeport (there have been many), it should accept alternate end mill holders and not be stuck at 3/8" diameter. End mill holders or R-8 collets are both options -- and not that expensive to purchase for your friend if he does not have them.

    You will probably do better with an adaptor arbor to accept horizontal milling cutters. Typical arbor diameter is 1", though there are smaller and larger diameter. A 1" arbor had clamping rings 1-1/4" diameter (and a key to keep the cutter from spinning on the arbor). It fits into the R-8 socket in the spindle of the mill. This produces a horizontal cut, so you will need the workpiece sicking out the side of the vise.
    Now -- for 1-3/8" depth of cut, we need to take half the diameter of the clamping rings (0.625") and add to that at least the depth of the needed cut (1-3/8") which brings us up to a 2" radius (4" diameter) thus eliminating the smallest common cutters, which are 3" diameter. The other size which I normally see is 6" diameter, which would be plenty for your task.
    Good Luck,         DoN.
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wrote:

And would never use them again. I'm not sure the brand and model of the mill - but it is european and the owner jokes he bought it from Noah's grandson.

And again, the tooling would likely never be used again - the mill is in the maintenance shop of a local leather products factory (belts) and is used to make tooling - I don't think they have added a "different" tool to it in 30 years - just replaced cutters as they wore or were damaged. I think all their tooling is Ti coated HSS - standard and short from 3/16 to about an inch diameter.

I am aware of that - I stated it would require a cutter of 2 inches plus the diameter of the arbour if I was going to do it on a horizontal mill, or on an arbour on my lathe - and the little horizontal mill that an old aquaintance used to have could only handle 3 inch cutters - he used it for cutting keyways in shafts and occaisionally making timing belt (toothed belt) sprockets..
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