interpolated helix using an electrode EDM?
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  1. #1
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    Default interpolated helix using an electrode EDM?

    I have a Timken bearing inner race (double taper)that is heat-treated. 2.437ID x 4" long I want to have a lubrication hole and helical groove to prevent the seizure onto a shaft. I can have the hole done by EDM but have yet to find a company that can put a helical groove on the inside. Any ideas out there would be appreciated.

    edm-helix.jpg

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    our EDM guy can cut threads, so I don't see why they couldn't do a helical groove.

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    Hi wea-sel:
    Yes this can be done; the whole trick is going to be making the electrode.
    Do you have a VMC with a fourth axis?
    If so you can make a trode out of Telco copper yourself and save a pile of money.
    Buy the copper at McMaster Carr.

    Your OD needs to be a bit less than the diameter of the bore so the trode can be dropped into the bore without touching anything, and your shape needs to be the inverse of what you want to get with some overburn allowance.
    For this job nothing needs to be very accurate, so just make something on the VMC and it will be good enough.
    Think of the trode as if it were an undersize and very coarse pitch tap.

    The EDM machine can then be programmed to orbit the workpiece around the electrode to bring the threadform out to diameter.
    Should take the sinker guy about half an hour to set up and about another half an hour to burn if you're not fussed about getting a nice finish.

    So long as you don't care where the start and end points of the helix are, this job is a cake walk and doesn't even need a C axis machine...any basic machine capable of orbiting can do this job.
    Maybe knock on RJT's door...he's in one of the Carolinas I believe and has a sinker more than capable of doing this job.
    Or you can just find a local EDM shop.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    The question is confusing.
    You want the shaft to rotate inside it's bearing?

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    Hi CarbideBob:
    I understood it to mean he wanted a helical oil distribution groove passing through his lubrication port ...I'm not sure why with the inner race of a Timken bearing.
    It looks like he wants oil to flow between the shaft and the ID of the inner race but since they don't move relative to one another during operation, I'm kinda stumped as to why??

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    You don't need a vmc with 4th. You can simply cut an elctrode with 2 side setups. Make sure there is enough over burn cut on the trode so it can enter the bushing. Nothing fancy, Mid-grade graphite is fine. I have done similar work before.

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    Good point SteveEX30:
    There is no need to make this trode fancy or accurate.
    You know, while I'm thinking of it, you could even make the trode by wrapping a heavy copper wire in a spiral around a mandrel and holding it at each end with a clamp and a screw.
    If the spiral is longer than the bushing, the clamps can hang out above the surface of the wire and it won't matter at all.

    One point; although graphite is the preferred material for most sinker guys, it is awfully messy to cut in a shop that's not equipped to manage the dust, so I personally would still go with copper if I was going to make the trode myself, just to keep the mess to a minimum.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Marcus I like how you think. Wound copper around a cylindrical electrode is a very interesting idea.

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    Hello CarbideBob,
    No, I do not want the shaft to rotate on the inside of the bearing. We still use the set screws to lock the collar onto the shaft. The shaft is stainless steel and the whole assembly is in a washdown environment with chemicals. Even though anti-seize is used in the assembly, after 3 months the bearing will have rusted tight to the shaft and will never come off without either destroying the shaft or bearing. Therefore, if there is a lubrication path that will allow grease to migrate or creep around the shaft it may help in bearing removal without destruction. Bearing race seizure onto a shaft is very common in industrial food processing equipment.

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    Marcus,
    I like what you said about wrapping a wire around a mandrel. So in a sinking EDM are you then orbiting the prepared mandrel around the inside of the race to make point contact? Multiple rotations or once around? I have seen wire EDM work but never electrode EDM. Would the copper wire be the consumable? One-shot use? Put a new wire on and do another one? We have Haas VMC's but no fourth axis. We have Hass lathes as well. I have contacted some local EDM shops and am waiting for a reply.
    Thanks

    Wes

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    Hi Wes:
    Orbiting is NOT rotation; instead how it works is that the electrode is made small enough that it can be put inside the bore without touching the sidewalls.
    Then the workpiece is displaced sideways in X until it burns the profile is as deep as it needs to be in that one spot.
    Then it backs up into the middle of the part.
    Then it moves sideways again but this time pointing in a new vector that is mostly the X direction and a little bit of Y direction.
    Then it goes back into the middle, then it goes out again a little bit less in X and a little bit more in Y.
    Then back to the middle.
    Etc etc until it has gone all the way around the inside of the bore.
    The part does not rotate.
    The electrode does not rotate.

    Yes the copper wire is the consumable, but it can often do a few before it is sufficiently worn to need replacement.

    If you do it by the twisted wire method. the way forward is to make a steel mandrel and two small collars each with a hole drilled through where the wire can go, and another where a setscrew can go.
    Put snap rings on the shaft so the collars cannot move toward each other, clamp the wire into one of the two collars and lock it with a setscrew, and then rotate the other collar relative to the first one until the wire is as twisted as you want.
    Then just lock that second collar with its own setscrew.
    That's it...set it up and start burning.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Hello Marcus
    Thanks for the clarity, So it's all x&y moves and small ones at that. I wouldn't want to write that program. So what would be a good clearance between trode OD and race ID? Who is RJT if I may ask? I've inquired into some local edm shops, two have declined and the last one 4x the price of a complete bearing.

    Thanks,
    Wes

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    Hi wea-sel:
    The EDM control writes the motion commands without you having to do anything except tell it how big you want the orbit to be.
    It's a super common function on every CNC EDM control out there.
    Typical clearance between trode and workpiece is maybe 0.010" to 0.025" per side but just about anything that's convenient will work.

    RJT is a toolroom owner in North Carolina who participates on this forum.
    Here's his web site:
    http://www.progtool.net
    He has sinker EDM capability and seems to build mostly tooling for production processes.
    I mention his name simply because I know he has a modern sinker and offers EDM as a service.
    His facility looks clean and modern and the quality of his work looks high to me.
    I don't know him personally and I have no idea if he would be interested in taking on your project.

    You may find someone who is closer to you and you really don't need a high end shop for this work.
    Any shop with a sinker capable of orbiting can do this; it is about as low tolerance a job as you can imagine.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Interesting project, Wes contacted me and we are looking into it. I see 2 options, make an electrode like a key cutter (full radius) and move it in a helix, or the wire wrap method and orbit Marcus suggested. With the wire wrap, i think we still would need to mill a helix around the arbor to let the wire rest in, and to be able to repeat and easily change wire, as it will erode as it is being used. Thanks for the recommendation Marcus.

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    All I want to know is how ever it is done... will some one please post a video of the process to some degree because I am blown away that this is possible. Maybe I'm sheltered and stuck in the 80's-90's but I am intrigued by this and would love to see it as would some others as well. Technology is AWESOME!

    Thanks,
    Tvalen1432

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    It really is basic. I would just cut the electrode in a side setup from graphite.
    Make sure to use enough over burn so the trode can enter the bushing. Circular orbit to size. Voila.

    It's a grease grove after all.

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    I know this is the EDM forum, but what's the reason for EDMing this part?

    The reason I ask is that it looks like it would be pretty simple to drop that bearing on a VMC table so the bore is aimed upward and then cut the groove using a lollipop cutter. Given that the groove will be very shallow the pressure on the tool won't be much, and the bore is wide open so you can use a larger cutter for strength. Drilling through the bearing race is easy enough as well with an AiTIN coated carbide drill, wouldn't take more than a few minutes... There would be some minor burrs to clean up, but a minute with a stone would take care of that. Given that this is just a lube channel I'm guessing that exact location and surface finish inside the channel is not critical? If exact location is not critical I would machine it in two operations (one from each side of the bore) to reduce the tool stickout needed...

    Just putting the thought out there as it seems to me like you could simplify the process by hard-milling it...

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