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Thread: router slot cut too wide! what is recommended tolerance for mitre slot slides

  1. #1

    router slot cut too wide! what is recommended tolerance for mitre slot slides

    I cut my 3/4" router slot on My band saw table/ I went for 3 passes ( by mistake) to cut the total depth. I accidentally cut it to wide. by 0.020".

    I figure the fix is to put UHMW tape in the slot. given the way it was cut I can only put the tape on one side. the only thing is, I don't know what is acceptable amount of tolerance. reason is i want to buy UHMW tape with the correct thickness.

    so how much tolerance is recommended (is it 0.002" 0.005?). I understand the proper way to do this is by feel but if I know before hand I can buy the correct thickness UHMW tape.

    thanks

  2. #2
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    What material is the table? If it is MDF or plywood, I would just glue in a hardwood scrap and recut the dado. If it is cast iron, you could use UHMW tape, and if it is too tight you could file or sand it until it glides with acceptable resistance. Not really sure what the recommended tolerance is.

  3. #3
    Quote Originally Posted by Cory filder View Post
    ...
    so how much tolerance is recommended (is it 0.002" 0.005?). ...
    Get in touch with your inner Engineer....Giigle for "sliding fit tolerances". This is one hit...https://www.engineersedge.com/class_i.htm and I've assumed you want the enumerated Class I fit.

    (Can't give you a number since I don't know your weights, speeds, length of engagement, distance to the opposite slot (if any), material(s), surface finish, etc..)
    Last edited by Malcolm McLeod; 12-03-2023 at 9:01 AM.

  4. #4
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    Quote Originally Posted by Doug Garson View Post
    What material is the table? If it is MDF or plywood, I would just glue in a hardwood scrap and recut the dado. If it is cast iron, you could use UHMW tape, and if it is too tight you could file or sand it until it glides with acceptable resistance. Not really sure what the recommended tolerance is.
    I would do the same thing.
    Lee Schierer
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  5. #5
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    There is no such thing as a a recommended tolerance but I would use the forecasting stone engineering evaluation process see image below.
    It goes something like this
    If it slides and chucks side to side it is too loose.
    If it doesn't slide or fit without grunting it is too tight
    If it starts out sliding but grabs half way down something is not parallel or bent
    If it slides in with like it was made for the thing and moves down the table like a sled on snow leave it alone it won't get any better.

    Like mentioned above close up the slot with a filler piece and recut. Or you can even leave it as it is and add the tape to your sled runner.
    calabrese55

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  6. #6
    Quote Originally Posted by Doug Garson View Post
    What material is the table? If it is MDF or plywood, I would just glue in a hardwood scrap and recut the dado. If it is cast iron, you could use UHMW tape, and if it is too tight you could file or sand it until it glides with acceptable resistance. Not really sure what the recommended tolerance is.
    baltic birch ply edge. hard to glue to that. Unless I hogged out a larger area and glue to bottom.

    Quote Originally Posted by Malcolm McLeod View Post
    Get in touch with your inner Engineer....Giigle for "sliding fit tolerances". This is one hit...https://www.engineersedge.com/class_i.htm and I've assumed you want the enumerated Class I fit.

    (Can't give you a number since I don't know your weights, speeds, length of engagement, distance to the opposite slot (if any), material(s), surface finish, etc..)
    Great resource. although the chart does cite bolts in holes. I can understand the tolerance changing because as the diameter of the bolt increases, there will be greater depth of the bolt. Is there a different chart for non hole?

    Quote Originally Posted by Lee Schierer View Post
    I would do the same thing.
    Quote Originally Posted by mike calabrese View Post
    There is no such thing as a a recommended tolerance but I would use the forecasting stone engineering evaluation process see image below.
    It goes something like this
    If it slides and chucks side to side it is too loose.
    If it doesn't slide or fit without grunting it is too tight
    If it starts out sliding but grabs half way down something is not parallel or bent
    If it slides in with like it was made for the thing and moves down the table like a sled on snow leave it alone it won't get any better.

    Like mentioned above close up the slot with a filler piece and recut. Or you can even leave it as it is and add the tape to your sled runner.
    calabrese55

    stone.jpg
    it will be hard to glue the end grain of the plywood. I will use the tape

  7. #7
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    It is easy to glue to the edge of baltic birch. I do it routinely. You should fill the whole slot with the plug, not try to make a .02" sliver to glue to one side.

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    Agree with Jamie, people edge band plywood everyday. I'd be more concerned that the tape might not stick or would be harder to position. Plus scrap wood and a little glue is cheaper than buying tape and you don't have to wait for delivery.

  9. #9
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    Perhaps go one step further.

    Widen and deepen the current slot, then make a filler of contrasting wood, and finally mill the correct size slot.

    Decorative rather than patched.
    Rick Potter

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  10. #10
    Quote Originally Posted by Rick Potter View Post
    Perhaps go one step further.

    Widen and deepen the current slot, then make a filler of contrasting wood, and finally mill the correct size slot.

    Decorative rather than patched.
    This would be my first, and second choice, without a third choice.

  11. #11
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    You don't need to get fancy with making the fit right. Start with the fit too tight, and when you open up the cut and the slide just starts to slide, stop cutting. There is no need to put a number on it. There is something about new woodworkers and their fixation with micro tolerances these days. I've nicknamed it the .005" club. I agree, it's easy to glue in a wood filler. It's not like the remaining shim will see a lot of load.
    Last edited by Richard Coers; 12-03-2023 at 7:24 PM.

  12. #12
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    Quote Originally Posted by Doug Garson View Post
    ...I would just glue in a hardwood scrap and recut the dado...
    This is the only sensible thing to do. The idea of buying some tape of precisely the right thickness to correct the screwup makes no sense at all.
    "Anything seems possible when you don't know what you're doing."

  13. #13
    Quote Originally Posted by Bruce Wrenn View Post
    This would be my first, and second choice, without a third choice.
    I understand the sentiment. but this is the reason. when you have experience, you know what is considered good enough. when you have less experience, there is more of a tendency to over build or overcompensate. I am in the latter category for now, but with time sure it will change

  14. #14
    Quote Originally Posted by Cory filder View Post
    I understand the sentiment. but this is the reason. when you have experience, you know what is considered good enough. when you have less experience, there is more of a tendency to over build or overcompensate. I am in the latter category for now, but with time sure it will change

    For all its importance, learning how accurate something needs to be (aka tolerance) is one of the more frustrating things to learn in woodworking. Especially since some things need to be super accurate, some things need to be kind of accurate, and some things just don't matter, and it isn't always obvious which it is. You can read as much as you want, but some things just require a lot of trial and error, usually a lot of errors, at least in my case

    Even more frustrating is when you combine tolerance with wood movement, and the drawers you spent two hours getting that "piston fit" and "whoosh of air" like they talk about in the glossy magazines, stop opening in June and are jammed shut until December.

    Back to your original question, another possibility is to get a miter track insert, Rockler, Woodcraft and others carry them. They are an aluminum track that standard miter bars fit into, and someone else has figured out the tolerance. The only problem is sometimes you don't have enough thickness of material for them, as they require a slot about 1/2" deep.

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