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IndustryArena Forum > MetalWorking > MetalWork Discussion > How would you cut these slots?
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  1. #1
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    Jul 2005
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    How would you cut these slots?

    I have a 1 1/4" (31.75mm) diameter steel rod with a series of cuts along the length. Each cut is approximately 2mm deep (at its deepest point), and about 1.65mm wide; which I believe makes a 45 degree angle when viewed from the side. There's a slot every 2.5mm (centre to centre) along the bar.

    Attachment 399956 Attachment 399958

    Attachment 399960

    I have an application where I'd like to reproduce this on a longer rod, and I'm wondering about the best way of doing it. I have a CNC machine - but it's really intended for wood/plastics/aluminium; though I have successfully cut 2mm sheet brass (albeit in several passes).

    I was thinking I could mount the rod along the length of my CNC table, and use a 45 degree bit to make each cut across the rod - likely in several passes. Does that sound realistic - especially without coolant?

  2. #2
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    Re: How would you cut these slots?

    Sounds like it would work. Carbide V-groove tool bit would be my choice.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Re: How would you cut these slots?

    Thanks Jim.

    I did wonder if they were originally cut using some sort of grinding wheel (it's the fence bar from an old British-made table saw). But given it's a 45 degree angle that wouldn't work with a cylindrical grinding wheel (even tipped at 45 degrees, the slot would have a 90 degree V-angle).

    What I haven't been able to find yet though is a 45 degree carbide bit. Searching for "45 degree" usually gets chamfer bits; designed for putting a 45 degree edge on stock - but the angle at the tip is 90 degrees.

  4. #4
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    Re: How would you cut these slots?

    Those are made on a horizontal milling machine or special machine, with a special gear hob. But, you can get 45 (22.5) degree engraving bits. Or these from Amana https://www.toolstoday.com/router-bi...uter-bits.html

    They could also be ground with a shaped wheel with a 45 degree included angle.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
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    Re: How would you cut these slots?

    hi there may be too much material for a bit : means long cycle time + fast tool wear; take a look @ attached tool / kindly
    Attached Thumbnails Attached Thumbnails DSCN0058.jpg  
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  6. #6
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    Re: How would you cut these slots?

    Quote Originally Posted by deadlykitten View Post
    hi there may be too much material for a bit : means long cycle time + fast tool wear; take a look @ attached tool / kindly
    Not going to be great on a vertical spindle machine, though, is it?

  7. #7
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    Re: How would you cut these slots?

    hy dharmic / yup, i know ... at least i show him a tool that delivers / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  8. #8
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    Re: How would you cut these slots?

    Thanks guys - I was vaguely aware of gear cutting machinery, but I've never come across a gear hob like that described above. Always good to learn. I assume they need a special motor + arbor, and aren't cheap!

    As for using a 45 degree engraving bit in steel (EN1A bright mild / SAE 12L14) how long would it realistically last? The amount of material being removed per cut would be small (2mm deep cut, approx 15mm long, but as it's across a round rod it's only 2mm deep in the middle). The issue would be that for the length I'm thinking of I'd need to mill something around 550 slots.

    A bit of experimentation in Sketchup tells me that a 2mm straight cutter would remove approx 32 cubic mm of material per slot. With the 45 degree bit I'd estimate it'd be around 20 cubic mm (0.00122047 cubic inches). For 550 slots that's about 11.000 cubic mm (0.67 cubic inches). Not much material for MDF or wood, but I guess steel is a very different story regarding tool life.

  9. #9
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    Re: How would you cut these slots?

    Quote Originally Posted by dharmic View Post
    Not going to be great on a vertical spindle machine, though, is it?
    I reckon it would be bl**dy awesome. Useless for my intended application, but still awesome

  10. #10
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    Re: How would you cut these slots?

    It would indeed be great. You'd need some kind of machine for it though, even a standard horizontal mill where the tools run out from the pedestal wouldn't work, it'd have to have an arrangement to drive the cutter oriented in a way that there was somewhere for the rod to go as it moved through its length under the cutter.

  11. #11
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    Re: How would you cut these slots?

    Quote Originally Posted by sploo View Post
    I was vaguely aware of gear cutting machinery, but I've never come across a gear hob like that described above. Always good to learn. I assume they need a special motor + arbor, and aren't cheap
    hy sploo / there is no need for a gear cutting machine ... those tools are not that cheap / cost depends more on tool geometry and required tool tolerance + hourly costs of your custom tool provider

    Quote Originally Posted by dharmic View Post
    it'd have to have an arrangement to drive the cutter oriented in a way that there was somewhere for the rod to go as it moved through its length under the cutter
    hy dharmic

    cnc : y lathe + hob holder ( tilted 90* )

    classic : there are some classical big mills, with strong horizontal spindle, capable of cutting with overhang > 0.5m; if tir is too big, then tool_active_length should be reduced ( less number of teeth = shorter or grinded tool, etc ) / kindly

    ps : my god, that baby is sooo freaky ...
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  12. #12
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    Re: How would you cut these slots?

    I did think for a minute about mounting a spindle horizontally, but of course the body would be larger than the hob cutter. Fine if you're taking one cut at the end of a rod. Not so good if you need to traverse over 1m / 3' down the length of a rod! I doubt my CNC machine would be rigid enough to handle it anyway.

    Returning to the idea of using a 45 degree milling bit, are there any tools/tables for estimating cutter lifetime (in material volume removed)? I've cut huge amounts of plastic and MDF over the years (though on a hobby basis - not commercial); as such a cutter lasts for ages so it's not something I've really considered. I don't know what would be realistic in steel; though I recently milled out about 9,300 cubic mm (0.56 cubic inches) in 2mm brass sheet with a cheap 4mm diameter spiral endmill, and it still seems good.

  13. #13
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    Re: How would you cut these slots?

    You could run a belt from your spindle nose twisted 90º onto an axle either mounted to the side running front to back or at the front running side to side, with a keyway etc in the axle to key a hob like the one deadlykitten showed. You'd need to machine the plates, bearing seats etc but I guess it needn't be /that/ huge of a job. Hob like that ain't going to run on a high speed spindle though, guessing it would be under 1000RPM.

    Deadlykitten - teh bebby was a silicone doll's head, shot with rim lighting only (no key or fill) against a black background with a stupid fast camera. Photoshopped for inverse and colourising. Back in the days when I was working for the government and all that counted was looking like I was busy at my desk.

  14. #14
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    ..........
    Last edited by deadlykitten; 08-21-2018 at 06:38 AM.
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  15. #15
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    Re: How would you cut these slots?

    Back in the days when I was working for the government and all that counted was looking like I was busy at my desk
    that job seems awesome / dream job

    if i may, how did you end up into the machining area ? maybe you should program remotely, and go back there; i wonder if you will look suspicious if anyone would heard you talking about chips / drills, etc

    ps : sorry 4 repeating : i posted from ind.arena during server meintenance and i guess it did not go well
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  16. #16
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    Re: How would you cut these slots?

    Quote Originally Posted by deadlykitten View Post
    that job seems awesome / dream job
    if i may, how did you end up into the machining area ? maybe you should program remotely, and go back there; i wonder if you will look suspicious if anyone would heard you talking about chips / drills, etc
    I've been a desk jockey (software/electronic engineer) for decades. The machining side of it started 18 years ago on one job for a small startup where none of the local machining shops wanted to touch a project I was working on unless I threw half of Australia's gold reserve at them and I ended up buying lathe, mill, grinder and a few other bits and pieces to do it in house. The bug bit and it's been a serious hobby since.

    In the last five-ten years I've picked up a few jobs which were less engineery, more designy and involved a lot more hands on workshop prototyping time. I'm actually back at college now doing an industrial design course on which to pivot my career. I want to get out of the soul sucking flouro lit open plan call centre office of despair and get into the workshop, get my hands dirty and make good stuff with good people that makes a difference to peoples' lives. Mostly, as my friends tell me, I just want to get paid to fvck about in my shed

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