can someone please help with hole dimensions

[komatias]

forgot to mention i want a close fit on the through holes so instead of 8.4mm i wanted 8.1mm thats what i meant to of said.

Ash

If you want alignment, use dowel pins or shoulder screws not plain screws. tightening the through holes will cause tolerance stackup issues.

[Clive S]

ahh yeah sorry i forgot about the position of the holes, as for the bottom 4 the reason why they are different is because the counterbore are on the opposite side. i do not have a dxf file as im new when it comes to drawing so that was actually my first drawing to show you guys lol.

cheers

Ash

Well then you have not said on the drawing which side is being countersunk. You have not mentioned 8.4mm only 8.1mm. If you say you want a hole for M8 it will probably end up at 6.8MM

So
1: Do you need 30mm ali
2: You don't need to say M8 just the hole size you want and whether it is through hole or to a depth
3: set all your measurements from two datum's ie bottom and one side.

[reefy86]

thanks guys, 30mm probably is ott what would you recommend for all round? i think i will stay with 30mm on the front z axis plate though but for everything else would 25 do? i know 20 is the minimum.

and with the holes so i just say 8.4mm through on plate 1 and 6.8mm tapped 15mm depth on plate 2?

Ash

[Clive S]

thanks guys, 30mm probably is ott what would you recommend for all round? i think i will stay with 30mm on the front z axis plate though but for everything else would 25 do? i know 20 is the minimum.

and with the holes so i just say 8.4mm through on plate 1 and 6.8mm tapped 15mm depth on plate 2?

Ash

How big is this machine I would have thought 20mm would have been enough for gantry ends and Z axis.
You said you wanted 8.1mm so now you are saying 8.4 !!!.
You have not mentioned plate number 2 If you want them to tap the holes just say tapped for M8 x 1.25 if that is what you want. You can't just say 6.8mm tapped

I would suggest you re do the posted drawing with the measurements as shown etc

[reefy86]

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

[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.