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  1. #31
    thank you. just dont want to be making any mistakes in my drawings and want everything to bolt together nicely the first time.


  2. #32
    ok, the precisionist in me is screaming right now because I work with drawings, precision and accuracy on a day to day basis.

    Everything has a tolerance, even ground shoulder bolts. A vernier caliper is not the golden standard as it has a 0.02+/- accuracy tolerance. A micrometer on the other hand is the standard. Would you need this kind of precision for your application? That is your decision.

    Now when you use a 12mm drill, you are likely to get a 12.1-12.2mm hole. If you want an accurate hole, you need to ream it.
    Stocking more goodies than just Smoothsteppers

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  4. #33
    Quote Originally Posted by reefy86 View Post
    thank you. just dont want to be making any mistakes in my drawings and want everything to bolt together nicely the first time.

    This is getting silly now just use standard cap head bolts like everybody else dose

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  6. #34
    Quote Originally Posted by Clive S View Post
    This is getting silly now just use standard cap head bolts like everybody else dose
    i dont mean to make this thread all pointless and silly, i have no real experience when it comes to cnc or mathmaticals unless its your typical diy timber frame that any dummy can do. now the cap head bolts was what i was using but then the shoulder screws came into it :). now ive read hundreds of threads and love them all and watched plenty of videos to know that there cant be any play in the machine regardless if its just cutting wood or aluminium so this is the reason why i asked about clearance hole size because when looking at the drill tap and clearance chart it tells me the clearance for an m8 bolt is 8.4mm but the bolt is 8mm so i asked if 8.1mm clearance hole would work and then i got told id get tolerance issues. everyone who is helping me here has their reasons and know what they are doing and i apologise for confusing people :)


  7. #35
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 3-4 years. Has a total post count of 593. Received thanks 79 times, giving thanks to others 5 times.
    Another way to look at this is that if you have access to high-precision machining and manufacturing facilities, you can make parts to incredible accuracy and just assemble. That's how car manufacturers work these days. If you are building with typical home workshop facilities, build with a bit of slack at key points and then align on assembly. That would never work commercially but with care and a bit of extra time, it can give good results. So I would go for 8.4mm clearance holes, for example, to give a bit more wiggle room on assembly. If you want to lock parts after setup, you could drill and ream through both components and fit dowel pins but I doubt if many do.

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  9. #36
    Quote Originally Posted by Boyan Silyavski View Post
    Shoulder screws are ground to specs, so a 12mm shaft shoulder screw is 12.00mm, see picture below. So i just drill a 12mm hole with a good new Dormer drill bit.
    You having a laugh.!! Drills are about much good at making accurate holes as I am at pole dancing.!! The whole point of Shoulder bolts is precision and this requires reamed holes.

    I've not commented here because Ash has been in touch via email so I've told him this already but I'll repeat again here for the sake of others reading this who are just thinking about building.!

    At DIY level building in lots of adjustment at the start is priceless when the machine built and your setting up chasing accuracy etc.
    With all the best will in the world and careful marking etc there is point that without High precision machinery to help with build then your always going to need adjustment or wiggle room.
    This doesn't mean high accuracy can't be achieved at DIY level it just takes lots of time and patience.

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  11. #37

    Keeping it simple - to bolt part A to part B with a flush fitting M8 cap head:

    1. If you are doing the work:
    Part A- scribe centre of hole, use centre punch, spot drill and then drill a through hole with diameter 8.5mm drill
    Part A- use an M8 counterbore tool (has diameter 15mm) to a depth of 8mm (same as M8 cap head depth)

    Part B- mark out, centre punch, spot drill, and then drill a pilot hole of 6.8mm diameter
    Part B- use an M8 x 1.25mm tap to create the thread (keep it straight in the hole)

    Tidy any raised burrs left on either side of part A or B using a countersink tool - otherwise they will not sit tight against each other
    __________________________________________________ _____

    2. If you are making a drawing for someone else to make:
    Part A- label hole circle as "dia 8.5", label counterbore circle as "CB dia 15x8"
    Part B- label hole circle as "M8 x 1.25" (they will know to drill it 6.8mm, tap it, and do the countersink tidy up)

    If you have multiple holes which are clearly all the same you can use " (xx places)" after the dimension. For example if you have 5 holes all the same you can label just one with the text "dia 8.5 (5 places)".
    __________________________________________________ _____

    Be aware that an M8 bolt is actually slightly less than 8mm in diameter so the hole could be 8mm but the 8.5mm clearance will give you some adjustment. I use 8.5mm (rather than 8.4mm) because 0.5mm steps come in the regular drill sets, although you can buy drills in various sizes such as 0.1mm steps.

    If for some reason when you put it all together that you need a bit more adjustment to account for slight errors in other parts, it is no big deal to drill the 8.5mm hole out to 9.0mm, so don't sweat the 8.1 vs 8.4 vs 8.5 dilemma. Important thing is to get a hole in the right place.

    If you have a more complex part with counterbores on the upper and lower surfaces (or any detail on other faces) then you need to draw all relevant views. To understand this read up about 3rd angle projection which is a standard for laying out the top, side, bottom, front, back, of any part in an unambiguous way that the machinist will understand.
    If you try to label a counterbore on the underside of the part by pointing to it on the upper surface drawing you will cause confusion and might get the CB on the top instead.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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  13. #38
    Spot onThat's exactly what I was trying to say very well put.

  14. #39
    thank you very much for that, as i mentioned to dean i was trying to make everything as zero tolerance as possible which for a diy machine its pretty much impossible to do that and was reading way too much into things so sorry for all the confusions :)


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