Cutting a Half-Round Slot

Got access to a router bit and bench drill? You could then make a simple router table using some wood jigs as a guide to maneuver the metal underneath the router bit.

Thank you very much. Yes, I have the mill, it's a question of the cutter. I'll try that one first. My way-out scheme was otherwise going to be to make a mixture of abrasive powder and epoxy and wrap it round a length of piano wire.

Do you not have access to a band saw or similar and can make the block width slightly wider to accommodate the material loss due to the cutting blade?

How about something in a dental bur?

Steel Burs - North American Rotary Instruments Inc.

Thank you. I had considered burrs, but so far only found limited sizes. i shall ask my dentist where he gets his from.

I seconded gringogreg's suggestion.

On another note, have you considered 3D printing with plastic? Maker Spaces with 3D printers seem to be abounding. Bayko looks like a neat system - I'm surprised someone hasn't already put out a file for them, but I didn't find one.

Indeed. i have a 3D printer, but my intention was to improve my metal machining skills.

Unless this is a really soft, and I mean really soft, metal you will destroy small mill bits or dental type burrs at an alarming rate.

Since you already have a milling machine then perhaps you have a boring head or fly cutter. If so you could easily make a holder to fit them that takes a carbide insert such as an SPG 432. That insert has a corner radius of 1/32" (0.03125") which is 62.5 thou diameter, but you could easily resharpen it to your required radius if this is critical.

I mention the SPG tip because it has relief, it will be easier to make a holder for it than say an SNMG tip, and it will leave the edges perpendicular to each other, a TPG or similar will not do this.

If you go this route, make the bar of sufficient length that the back of the insert clears the cut during rotation

Failing that option, get a larger HSS 4 flute end mill and resharpen it with a 75 thou edge radius.

I haven't looked but there may be sprocket cutters for small chains that have 0.075" rollers. Say no more.
Jim

Thank you. I rather like that idea.

I take it from comment #9 and your reply that these grooves are not on the edges as I understood the question to imply, but on the faces, so please disregard my obviously erroneous earlier post as none of that would work for a groove down the face of the block. Never having sighted these blocks I assumed they were indeed edge grooves that you required.

This is the set-up, the grooves will be to take the rods that support the structure. I can remember having this toy when I was small & before I was tempted away by Lego.

Bayko builders set... We had that as kids...

Anyone remember Flexo ? (can't find a picture of it on google) it was a load of plastic pieces each about 1" x 0.5" each being a rectangular frame of plastic with cross braces (bit like a union Jack) each corner had a small round tab with either a hole or a peg so they would could be joined together.

Same era as Bayko

Del

I am with Nigh but suggest filing or sawing a nick in the sides before putting together and drilling. The drill will follow the groove.

If it is more than about 4 drill diameters in depth, the drill will wander. Milling the slot is a better solution. There are end ball end mills of about any diameter you want - but that diameter will be fragile. You can also use a profile cutting tool - think circular saw blade - that will be much more robust.

Ok what about mounting the brick in a 4 jaw chuck and mounting a dremel on the cross slide. Clamp the chuck and traverse the tool across.

GA from me, my thoughts exactly.

Id like to broach the subject of maybe using a broach.

Del

You can wear whatever jewellery you like.

You could try making your own cutter from a piece of 1/2" or larger drill rod (I think the Brits call it silver steel?). Use a lathe and cut the profile in the shaft, then use your mill to cut the front of the cutting edges. Carefully mill or hand file the back relief. Now you will have several cutting edges like a miniature circular saw blade on a very stiff shaft. You could probably get away with one tooth. Harden your custom tool, and start production.

If you have a boring bar you could also grind the point to the profile you want. I have some carbide tipped boring bars that sharpen nicely with diamond wheels - I think Dremel has some small diamond embedded grinding wheels.

Making custom cutting tools is not difficult.

What tools do you have at your disposal?

Mill, Lathe, drill press, saws?

Mill and small lathe, Dremel tool, hand saws. I'm happy with sharpening lathe tools had not thought of grinding a round cutter myself.

With your tooling you can easily grind a boring bar to the profile you want and use it as a fly cutter in the mill.

If you have a vertical mill, your work piece would be held horizontally (parallel to the table) to cut the groove on the side as the table traverses. You will need a spacer under the work piece to give your cutter clearance. Clamp your pieces vertically onto the spacer and the table. I don't think you could clamp the edges in a standard table vice.

If you have many pieces you may want to clamp your spacer with stops to align each piece without having to tram each one for parallel. Another idea is to cut your groove in a long piece of stock, then cut that into pieces for each item - saves setup time.

(As an aside example - I needed a left hand 5/16 x20 tap - so I made my own tap - cut the thread on the lathe, milled the slots on the mill, hand filed the relief on the back side of the cutting edges, then hardened the drill rod - worked like a dream!

If you need a small groove on a shaft you make your own profile cutter for the lathe - same deal for a cutter for the mill.)

I really am most grateful for all the advice I have been given, including the encouragement to grind my own cutting shapes. If that works i will have made a massive step forwards in my humble workshop.

I am basically a "Hobby Machinist". I find the challenge of making my own tooling half the fun.

You sound new to hobby machining. I assumed you know how to tram your vice or work piece get parallel faces. Tubalcain has some excellent Youtube clips on machining.

My current project is adding Jenex Digital Read Out (DRO) to the mill. I have the X and Y done and am doing some design work to add the Q axis (Quill). I think I may regret only getting 3 axis and not four - I could probably have used the Z axis also. I see many of the mills that get modified for CNC use the Z axis instead of the Quill. Probably there is less play and more travel in the Z axis. Only my Q axis had a power feed and vernier read out, but when they add the CNC the Z axis automatically gets an encoder. I will change to ball screws before going CNC - an attempt to fly the cost under the radar of "the boss".

I still reckon it would be easy to make a holding/guiding jig and a broaching tool.

You aren't removing much material, and after all, if it's good enough to cut the rifling in a Kentucky long rifle, I think it will manage an inch of metal.

But nobody listens to me, I'm just a cat Bwahhhhhh

Del

(Tumbleweed rolls past as Del sits tucked up staring patiently waiting for a response)

I don't know how you envisage using your broach but i could see a parting tool with the end ground round, held 90 deg to the normal position in the tool post and then wound across the job like a shaper. With the job held in a 4 jaw chuck. The compound slide can increment the depth whilst the cross slide does the work.Jim.Now please get up off that rock and go chase down that tumbleweed. I need another cat video to post to U tube. There just aren't enough cat videos.

Yeah, broach mounted on cross slide would be good.

Effectively same as you suggest but with successive teeth each a couple of thou deeper (or consistent tooth depth and the tool slightly angle. It could probably cut a good depth in one traverse.

GTG... tumbleweed

Del

Might want to try googling Iscar solid mini micro tools - appartently available in sizes less that .2mm(.0078")