can someone please help with hole dimensions

[Clive S]

above post mentioned tolerance stackup issue with tighter holes which is why i went back to 8.4mm. plate 2 was me trying to say i want a m8 cap screw to go through plate 1 and then screwed into plate 2 which is tapped ect. i apologise for my bad explinations. and machine cutting area is 8 x 4.

cheers

Ash

Have you put a drawing up about the machine gantry etc? Dean might be best to comment on plate thickness.

Bullet points are the best on separate lines to stop confusion when asking a question (just be blunt)

[reefy86]

just a quick one. if im using shoulder screws do i do the through holes 10mm which is what the shoulder screw is or do i make it slightly bigger like 10.1mm. dont want to make a mistake of inserting 10mm shoulder into 10mm hole and it gets stuck ect

[komatias]

Ok, shoulder bolts are ground to specific tolerances on the shank. Depending where you get them from, there will be a tolerance class to them like h8 or something. That will tell you what hole size and tolerance you should specify depending on the tightness of the fit you want. Give us a link to the bolts.

This is where geometric tolerance will also come in to play but that may be overkill for your application.


Are you looking to get this made by a chap in a shed or are a pro machine shop?

[reefy86]

just in general i was checking ebay out for the shoulder screws

http://www.ebay.co.uk/itm/10mm-M8-SO...DKYqt_xV0EeV8A

states nothing about tolerance just simple dimensions ect. although here it has more technical info but £3.44 per screw jesus lol.

http://www.shoulder-screws.co.uk/?gc...LnEaAskt8P8HAQ

[Boyan Silyavski]

just in general i was checking ebay out for the shoulder screws

http://www.ebay.co.uk/itm/10mm-M8-SO...DKYqt_xV0EeV8A

states nothing about tolerance just simple dimensions ect.

Ash

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.

[reefy86]

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

Ash

[komatias]

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.

[Clive S]

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

Ash

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

[JAZZCNC]

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.

[routercnc]

Ash,

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)".
__________________________________________________ _____

Notes:
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.