Screw size for Parallax robots [SOLVED]

David BetzDavid Betz Posts: 14,179
edited 2020-01-13 - 17:00:37 in Robotics
What size screws does Parallax use for their ActivityBot? I'd like to order some additional screws and I want to make sure I order the same size. I'm thinking they are #4 40 screws but the pictures of those that I find on Amazon look larger than the ones in my ActivityBot. What size does Parallax use?
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Comments

  • Never mind. It looks like they are #4 40 screws.
  • M3x0.5, one hopes.

    I've never understood the imperial screw numbering, the numbers don't seem to have any meaning of themselves.
  • David Betz wrote: »
    Never mind. It looks like they are #4 40 screws.

    That's the size I used to hold the servos on the bot I assembled. Currently he's using a BOE as his brains. Next up, is the PAB design. POF (Point Of Fact) I think the frame was intended for an activity bot design.

    Yes understanding the regular standard for machine screws takes time. It took me two whole semesters in high school to understand the whole business behind them. However I find understanding the Metric standard for the screws used by the bots who surface wearing directly an Arduino for the same purpose difficult.
  • evanhevanh Posts: 9,985
    edited 2020-01-09 - 02:26:45
    How is 3 mm diameter x 0.5 mm pitch difficult to understand? Choosing a 3.5 mm or 4 mm drill bit to suit is simplicity.

    EDIT: Or of you want it really snug for the top holes, say, then a 3 mm drill bit. And for tapping, use a 2.5 mm drill bit.

  • evanh wrote: »
    M3x0.5, one hopes.

    I've never understood the imperial screw numbering, the numbers don't seem to have any meaning of themselves.
    Are you saying that M3x0.5 is the same as #4 40?

  • No, the sizes are visibly similar is all. Imperial stuff is so old, I wonder why anyone still uses it.

  • evanh wrote:
    Imperial stuff is so old, I wonder why anyone still uses it.
    Here in the States, UNC and UNF are still the most common systems for fastener sizes. Ubiquity breeds more ubiquity. And as long as it's still universally accepted, there's really no reason to change. Neither system has inherent superiority over the other. In both metric and imperial systems, the fasteners hold like they're supposed to. What else matters?

    -Phil
  • Lol, straight after I demo'd how much easier metric screws are to work with.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,760
    edited 2020-01-09 - 05:56:22
    evanh wrote:
    Lol, straight after I demo'd how much easier metric screws are to work with.
    Oh, right:
    How is 3 mm diameter x 0.5 mm pitch difficult to understand? Choosing a 3.5 mm or 4 mm drill bit to suit is simplicity.
    If you even have any metric bits at hand. A trip to the hardware store, perhaps? Or just look up the equivalent letter, number, or fractional drill size from that handy card you keep in the drill drawer. Same routine as for UNC and UNF, except wait! You only have to do that for #6 and #8. #4 is 1/8", #10 is 3/16", and sizes above those are all fractional inches. Nothing to look up, and you already have the bits.

    Then there are the tap drill sizes. No advantage there for metric. It's still an exercise in consulting a chart and finding the correct number or letter drill.

    -Phil
  • Well, of course, we generally only have metric tools here. It's a special trip to get oddball imperial stuff for machines that were discontinued in production in the 1970's.

  • Then there are the tap drill sizes. No advantage there for metric. It's still an exercise in consulting a chart and finding the correct number or letter drill.

    For tapping metric, it's simply M3 - 0.5 pitch = 2.5 mm drill bit. Another example, M4 x 0.7 pitch is 4 - 0.7 = 3.3 mm drill bit. Easy as.

  • evanh wrote:
    Imperial stuff is so old, I wonder why anyone still uses it.
    Here in the States, UNC and UNF are still the most common systems for fastener sizes. Ubiquity breeds more ubiquity. And as long as it's still universally accepted, there's really no reason to change. Neither system has inherent superiority over the other. In both metric and imperial systems, the fasteners hold like they're supposed to. What else matters?

    -Phil
    What do UNC and UNF refer to?

  • According to the Industrial Arts teacher from that high school, they describe either how course the thread is, or how fine they are. Typically the course threaded ones are the much larger ones, 1/4-20 for example. But the one's we are concerned with, which is the 4-40 size is the fine threaded one.
    ----
    And there the mascot offers, "What this world needs is more sleep!", he said sleepily.
  • David,

    UNC means Unified National Coarse and UNF means Unified National Fine.

    Does this by chance have what you need?
    https://www.parallax.com/product/570-35000
  • Genetix wrote: »
    David,

    UNC means Unified National Coarse and UNF means Unified National Fine.

    Does this by chance have what you need?
    https://www.parallax.com/product/570-35000
    Yes, that has some of what I need but I wanted to order a screw assortment rather than just a refresh kit for the ActivityBot. However, the description of that item confirms that the screws are in fact #4 40 which is what I needed to know. Thanks!

  • evanh wrote:
    For tapping metric, it's simply M3 - 0.5 pitch = 2.5 mm drill bit. Another example, M4 x 0.7 pitch is 4 - 0.7 = 3.3 mm drill bit. Easy as.
    Well, I admit, that does simplify things. It looks like that's for 100% thread depth. For a looser fit, I guess you just add 0.1mm or so. Do metric drill indexes come with bits in steps of 0.1mm?

    -Phil
  • Genetix wrote: »
    David,

    UNC means Unified National Coarse and UNF means Unified National Fine.

    Does this by chance have what you need?
    https://www.parallax.com/product/570-35000

    That's basically what I posted, I didn't go into that kind of detail, because that same teacher then did not either.
  • I usually do not put oil on fire, but this imperial nonsense here in the US of A drives me nuts.

    And it is not even a either or, try to put a Gate Opener on a Gate. Gate is imperial, Opener uses metric, lock uses both.

    Last week I opened my 220 piece craftsmen set the wrong way around and ended up with about 190 pieces on the floor.

    Getting the metric ones back in was easy, they are simply ordered by ascending numbers. The imperial ones - well - might still be in wrong order where the ffff belongs 9/16 or 5/56 this is literally nuts.

    Same goes for weights. There is no L no B or no S in the word pound. Ounce does not contain an Z, the list goes on and on. Wire diameters in gauges, alike bullets the diameter is how many balls one can make out of one pound of lead.

    Really?

    I had to buy gravel for my drive way, I expected a question for cubic inch or cubic foot, but no I was asked how many YARDS I would need. Yards.

    Try to work on ANY American car and you will have a mix of imperial and metric, because outside of the US nobody uses imperial so everything not made in the US is metric.

    Mike
  • It is still the case in the US that if you go to a retail hardware store the metric wares are relegated to a single cabinet at the back of the fastener aisle, with a limited selection, usually only one grade and coarse thread. The imperial fasteners will be available in both UNC and UNF and in harder grades for when more strength is required. And the only thing worse than imperial measurement is mixing imperial and metric fasteners on the same project.

    By the way, the designation #4-40 refers to the hole diameter and the thread pitch, so this would be a #4 hole (that the fastener passes through, not a tap) and 40 threads per inch.
  • It looks like that's for 100% thread depth. For a looser fit, I guess you just add 0.1mm or so. Do metric drill indexes come with bits in steps of 0.1mm?
    That's loose enough I've found, not that I'm any machining shop expert. I tend to go the other way for a tighter fit on soft/thin materials.

    0.1 mm steps is available as singles at least. The common small drill sets go in steps of 0.5 mm at the low end and bigger steps at the larger sizes usually. I've never shopped for any "craftsman" set.

  • Another thing about imperial stuff, drill bits. For about $50 on sale you can get a >100 piece drill bit set from Harbor Freight that has all the number and letter sizes as well as the standard inch sizes from 1/16 to 1/2 by 1/32 inch increments. The gauge sized bits are much more finely incremented and comprise more than 2/3 of the set. Those sizes increase exponentially with the gap between sizes being roughly proportional to the sizes themselves and were established by experience, so I'm not sure what translates to them in metric world. You will find on tapping charts that a number or letter size is often the best fit, and when sizing things "by feel" you can almost always get something that is as close to exactly what you want as you can perceive.
  • localroger wrote:
    For about $50 on sale you can get a >100 piece drill bit set from Harbor Freight that has all the number and letter sizes as well as the standard inch sizes from 1/16 to 1/2 by 1/32 inch increments.
    I have one of those sets, purchased years ago from Costco. I still have all of the bits, too, except three of the smallest number-sized ones that got broken. They're good-quality bits, too, with a titanium nitride coating.

    My only major peeve with the UNC/UNF system is with #10 machine screws. I can't count the number of times I've gone to the hardware store to get, say, some 10-32s, and find a 10-24 in the assortment once I get home that was wrongly binned. Drives me nuts!

    -Phil
  • The only reason I can see for choosing imperial over metric fasteners for a product is availability, and if it is to be sold world wide metric is the way to go. The sizes and pitches are well thought out and cover a wide range with a smaller number of nuts and bolts which reduces the number of item bins that need to be inventoried. For instance all the nut/bolt sizes up to 1.5 inches/39 millimeters would require 47 bins for imperial UNC/UNF while metric coarse/fine requires only 31. That's a big saving in parts and space.
  • localroger wrote:
    It is still the case in the US that if you go to a retail hardware store the metric wares are relegated to a single cabinet at the back of the fastener aisle, with a limited selection, usually only one grade and coarse thread.
    I guess I'm lucky. The hardware store in my little town of 7000 folks has a thorough selection of metric fasteners. Here's a photo that outlines their metric section:

    metric_fasteners.png

    The selection includes zinc-plated steel and stainless steel screws, bolts, and nuts, steel bolts and nuts in various hardness grades, T-nuts, coupling nuts, socket cap screws, jam nuts, lock washers, and a host of other fastener styles. They also carry metric drill bits, taps and dies in another part of the store.

    The "imperial" section, of course, is much larger, comprising two entire aisles, floor-to-barely-within-reach. It includes screws ranging down to #0 on up in plated steel, stainless steel, bronze, brass, and colored finishes, in multiple hardness grades. And to top it off, this cornucopia is only a few blocks from my house (handy for plumbing jobs that require, on average, three trips to the store :) ).

    Of course, their stuff is not cheap. My brother, who was in the hardware biz for decades, said that fasteners have the highest markup of any products in the store. So for bulk purchases that I can wait to receive, I order online from McMaster-Carr or microfasteners.com. But for onsie-twosies, the local store can't be beat. I'm pretty sure they even put Lowes and Home Depot to shame.

    -Phil
    800 x 454 - 892K
  • I just ordered and received an assortment of #4 40 screws from Amazon and they seem to be exactly the same size as the ones that came with my ActivityBot.
  • David Betz wrote: »
    I just ordered and received an assortment of #4 40 screws from Amazon and they seem to be exactly the same size as the ones that came with my ActivityBot.

    No surprise there. The imperial UNC and UNF nuts and bolts available are generally of very good quality and consistency.
  • Phil,

    Are those mixed-thread #10 screws from China?

    Last time I ordered screws from McMaster-Carr a number of years ago they were made in Taiwan.
  • Gentix wrote:
    Are those mixed-thread #10 screws from China?
    Probably. They don't get mixed at the source, though. It usually happens when a customer or employee returns a screw to the wrong bin or drawer. I've gotten in the habit of grabbing a nut and testing each #10 screw before I put it in the bag.

    -Phil
  • Phil, that's impressive. There are no hardware stores around here that good. Still, "putting Lowe's and Home Depot to shame" is a pretty low bar to clear, as they don't like to stock anything that doesn't move quickly, but it's hard for a proper hardware store to compete with them on the stuff that does move quickly.
  • Screw trivia.

    For numbered screw series, the major diameter = 0.060 + num * 0.013. So a #4 screw diameter is 0.112. (0.060 + 4*0.013)


    -Russ
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