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  1. #1
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    Default Best technique for cutting slots in SHS

    I've offered to help a mate out by machining some pieces of 75x4 SHS for him.
    They are outer sleeves with 19mm slots and a section removed from the side to allow it to clamp over another piece of SHS with an 18mm bolt.
    Pieces are approx 150mm long.
    Not a precision job but he needs a dozen of them and I'd prefer not to take a whole day making them!

    Thinking I might just grab a 19mm or 3/4" endmill to cut the slots, flip the part 90deg and use the same cutter to rip the section out of the back side leaving a small tab on each end so it doesn't spring/collapse on me. Finish off with angle grinder and cutting disk to remove the tabs and flapper wheel to round the corners and deburr.

    I'm interested in how you experienced guys would tackle this from a more production perspective.

    Outer Sleeve.JPG

    Steve

  2. #2
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    Default

    That's how I have done similar jobs in the past with SHS & RHS, used a 3 flute cutter so I could plunge cut. Make sure that the seam face is the one that ends up being removed at the last pass and it will look quite tidy.
    Quick and easy.

  3. #3
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    By all means use an end mill to cut the 2 captive slots, but it would be far quicker to use an angle grinder with an abrasive disc to make two full length cuts to take the slot out of the other side.

  4. #4
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    Hi Steve, Guys,

    What others have said, in addition, I would leave the material in one piece and set up the mill to step and repeat for each slot, turn over and repeat for the other side. Cut into chunks and take the piece out of the seam side.

    Actually I would use the bandsaw to cut the waste side out. Again a step and repeat job.
    Best Regards:
    Baron J.

  5. #5
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    plasma cutter with guide?
    Gold, the colour of choice for the discerning person.

  6. #6
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    This is your opportunity to justify the purchase of that 5 Axis CNC...

    Me.. Id fixture the table for repeatable, mill the slots, cut the centre out with a grinder and round the ends with a resin fibre disc (cheaper and more effective than a flapper)
    If you can, cut the seam out when you remove the centre section

  7. #7
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    Quote Originally Posted by OLCDOG View Post
    By all means use an end mill to cut the 2 captive slots, but it would be far quicker to use an angle grinder with an abrasive disc to make two full length cuts to take the slot out of the other side.
    Thanks OLDCDOG - likely quicker for the cut, but I'm dubious about my ability to make a nice straight cut for that length - and end up with a mess that takes more time to clean up to get looking nice afterwards. I'll give it a try though.

    Quote Originally Posted by BaronJ View Post
    Hi Steve, Guys,

    What others have said, in addition, I would leave the material in one piece and set up the mill to step and repeat for each slot, turn over and repeat for the other side. Cut into chunks and take the piece out of the seam side.

    Actually I would use the bandsaw to cut the waste side out. Again a step and repeat job.
    Thanks John. Bandsaw or any non-abrasive cutoff saw would be nice to cut the side out. I've only got the vertical bandsaw and the power hacksaw. Hacksaw would likely end in tears even if they would fit in the vice (which I don't think will). Not sure I've got the clearance for a full vertical cut in the bandsaw, and the variable pitch blade probably isn't ideal for a 6" cut. Some sort of an angle plate to lay the part back slightly might solve both the clearance and cut length issues.

    Quote Originally Posted by .RC. View Post
    plasma cutter with guide?
    Thanks RC - but with me doing it (even with a guide) I'm sure the slots would look like they had been chewed out out by a pack of rabid rats!!
    Could be workable for the the straight cuts on the seam side though. Worth a quick test anyway.

    Steve

  8. #8
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    I’d mill the slots and cut the side, imagine milling that and it closed up on your cutter! bang!

  9. #9
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    Quote Originally Posted by racingtadpole View Post
    This is your opportunity to justify the purchase of that 5 Axis CNC...

    Me.. Id fixture the table for repeatable, mill the slots, cut the centre out with a grinder and round the ends with a resin fibre disc (cheaper and more effective than a flapper)
    If you can, cut the seam out when you remove the centre section
    Hmmm. I can see it now.....
    "I've got no idea what happened. Last thing I remember I was discussing something with my wife - and when I came to I was lying in the paddock, my shed was on fire, my wife is missing and I've got this strange note that says -- that just cost you half --"

    Resin fibre disc, I don't know much about them. From having a quick search they look like a larger version of the 3" 3M Roloc sanding discs I used in the '90s when I was still on the tools. Will suss them out but if you've got any particular recommendation or info would love to hear more.

    On the fixturing in the mill, my vice is 6" so I should be able to just set the spindle on the centreline of the SHS, clamp the part flush with one end of the vice and use the DRO for the start and finish points. Rotate the part 180deg and slot the other side. Rinse and repeat.

    Steve

  10. #10
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    I used to make a part almost identical to that, it was for a spare wheel swing arm on a rear bar for a 4wd.

    I didnt have a mill, so I drilled out the ends of the slots then cut the rest of the slot with the plasma cutter and cut the section out of the tube the same way. A quick clean up with a file and grinder and the jobs done. I always made sure the section cut out contained the seam

    Cheers Andrew

  11. #11
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    Hi Steve, Guys,

    Some interesting posts and techniques in this thread.

    Thanks John. Bandsaw or any non-abrasive cutoff saw would be nice to cut the side out. I've only got the vertical bandsaw and the power hacksaw. Hacksaw would likely end in tears even if they would fit in the vice (which I don't think will). Not sure I've got the clearance for a full vertical cut in the bandsaw, and the variable pitch blade probably isn't ideal for a 6" cut. Some sort of an angle plate to lay the part back slightly might solve both the clearance and cut length issues.
    I would simply clamp the tube to the mill table for milling the slots. Set a stop so that you are not milling the slot at an angle and clamp it down.

    Yes I'm spoilt since I got a bandsaw. A piece of wood to cant the work piece up a little in the vise and have at it. I've used that trick a few times, as long as the blade cannot flip the work up and you keep an eye on it because the knock off wont stop the saw without cutting into the bottom edge of the work piece.

    Though I do like the plasma cutter idea !
    Best Regards:
    Baron J.

  12. #12
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    I use the flexovit discs, available from the red and green

    https://www.bunnings.com.au/flexovit...-disc_p6330354

    Also a one off purchase of a backing plate required at around $20ish for a decent one, mine is Bosch.

  13. #13
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    How about you hold the SHS open while cutting? I first through of a tapered piece of wood hammered in there, but I think a pair of tool makers clamps setup to force things apart would be more refined. Even a bolt the right length with a nut "undone"inside the SHS might do the job.

    If I was making a lot I'd come up with a way to do it on my Hoz bandsaw. For a doz I think I'd just mill them.

    If you go the grinder to finish route you could take a 2mm deep cut on the ends to give you a nice straight edge to run the grinder alot.

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