Deep but narrow blind slot

This topic has 15 replies, 13 voices, and was last updated 23 March 2026 at 19:10 by Grizzly bear.

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22 March 2026 at 12:15 #841883
colin hamilton
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@colinhamilton16803
I would like to cut blind slot in the end of a shaft (in the end face if the shaft). The slot needs to be contained within the diameter of the shaft. The cross section of the slot is approximately 20mm by 3mm and I would like it at least 20mm deep. 20mm deep looks way beyond the 3mm end mill i have. What would be the best way of going about this?

Thanks Colin
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22 March 2026 at 12:21 #841884
Durhambuilder
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@durhambuilder
Could you machine the end of the shaft smaller than required, cut a slot right across with a slitting saw and then shrink or silver solder a sleeve around the outside to bring back to final required diameter?
22 March 2026 at 12:28 #841886
Robert Atkinson 2
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@robertatkinson2
Bit lacking on information. What material? What equipment do you have? How long is the shaft?

EDM is one option. Failing that you can get long mills..
22 March 2026 at 12:51 #841890
Tony Pratt 1
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@tonypratt1
A bit of context is needed as this is really only easily doable with EDM if indeed the part is metal, why so deep and narrow? Can the part be redesigned for ease of manufacture?

Tony
22 March 2026 at 13:51 #841893
peak4
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@peak4
A bit lacking on context, material, and size

Mill a slot in the side of the shaft, go in with a T-slot cutter, silver solder a bit of metal in the original slot and skim the outer diameter.

Bill
22 March 2026 at 14:38 #841897
not done it yet
Participant
@notdoneityet
Why a blind slot? If side loaded at the ends, it might make the choice between the Durhambuilder and peak4 options (if going that way) more obvious.
22 March 2026 at 15:01 #841906
old mart
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@oldmart
I would do it with a 3mm solid carbide end cutting mill, in lots of careful stages being careful to remove all of the swarf each time. By stages, I mean 0.5mm increments which will lessen the danger of breaking the mill. Another way would be to remove most of the metal with a line of chain drilled holes of 2.7mm if using HSS drills or 3mm if solid carbide drills, followed by milling. This would still require very careful progression. The finished slot would not have a perfect surface finish, and the ends would have a 1.5mm rad.
22 March 2026 at 15:08 #841909
cedric 1
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@cedric
Redesign your part so it’s easier to machine. There is always more than one way to skin a cat. What you are proposing, a 3mm closed-end slot 20mm deep, is going to be difficult, albeit doable given enough patience. It might be far easier to eliminate the need for the awkward slot and use a simpler, easier yo make design.
22 March 2026 at 15:59 #841916
Dave S
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@daves59043
Chain drill with a 2.5mm 10D carbide drill to remove the bulk of the material.

Then I would plunge cut the majority of the slot with a carbide 3 flute, if possible undersized like 2.8mm

Then machine the walls to clean up

Dave
22 March 2026 at 17:27 #841927
DC31k
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@dc31k
Any milling solution will be made more difficult by swarf removal.

Turning the head of the mill sideways, having the shaft horizontal and starting at the bottom will allow swarf to drop away, as well as facilitating access for a blow gun to keep the cavity clean.

The shrink fit sleeve is a good suggestion, but we would need to know the diameter of the shaft. 20mm long in a 25mm diameter item is different to 20mm long in a 60mm diameter item.
22 March 2026 at 18:21 #841940
bernard towers
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@bernardtowers37738
Im with Durham Builder all the way.
22 March 2026 at 19:02 #841950
Grizzly bear
Participant
@grizzlybear
Hi,

Why don’t people state its intended use? (Or did I miss it?).
22 March 2026 at 20:33 #841965
colin hamilton
Participant
@colinhamilton16803
Sorry everyone for the lack of context. I’m looking to make a set of rotating skewers for my grill. So its basically going to be a series of gears where the shaft sticks out a way with the slot cut into the end of the shaft. The idea being the kebab skewers are placed into the slot and rotate (I will make some sort of support on the other side of the grill for the handle end of the skewer). I’ve never cut gears before and that is going well. Everything is made of EN3b. The gears are all module 1.5. The gears for the kebabs are 36tooth. I’m going to need to add a couple of speed reduction gears as my motor is running at 40rpm. The bearings I’ve got have a 15mm bore so I was going to drill and tap the ends of the shaft and after the gearbox is assembled i will screw in a bigger diameter section with the slot. I like the idea of cutting the slit all the way across and the silver soldering a sleeve round after. I did some silvering soldering for the first time today as I’m soldering the gears onto the shafts
23 March 2026 at 06:23 #841976
cedric 1
Participant
@cedric
<p style=”text-align: left;”>To rotate a kebab skewer? Is it the type with a round ring on the end? If so, just support the shank of the skewer with a bit of sheet metal with a V notch cut in it. Then just cut a slot all the way across your drive shaft with a slitting saw.</p>
23 March 2026 at 09:45 #841990
Bazyle
Participant
@bazyle
If it is a kebab skewer with a loop on the end just screw a cup hook into the end of the shaft. Your precision engineering route will give you all sorts of alignment problems.
23 March 2026 at 19:10 #842099
Grizzly bear
Participant
@grizzlybear
Hi Colin,

Thanks for the update.

Good luck………
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