Reply To: How accurately can you machine?

[Ex contributorParticipant @mgnbuk]

Is it only me that often turns things exactly 0.5mm wrong when using a metric micrometer. Pestilential things, use a digi caliper to get near then switch to the mike if that sort of accuracy is needed.

Nope, happens to me too & I have taken to checking the mike with a digital caliper to make sure I'm not 0.5mm out. Frequently get asked by operators at work to check a Metric mike reading for this – they also have digital calipers & don't think to use these as a quick check on the mike for confirmation.

Don't seem to have the same problem with Imperial mikes & have a poundshop large button calculator double-sided taped to a cabinet above the lathe for instant conversions when the 0-1" is to hand & Metric dimension required. The Polish 0-1" mike was a subscription "gift" with ME or MEW quite a few years ago – pity such useful "gifts" are not offered these days. I have Metric mikes to 100mm & Imperial to 6", so can measure most things I can fit in the lathe. These are not "officially" calibrated & most are used (some of the Metric are "new old stock" DDR made, with standards) but a check with a slips set from work suggest they are all pretty close – though should an accurate measurement be called for I would be wanting to check more carefully. Like others above have said, most times use a digital caliper (Aldi / Lidl) while roughing out & mike to finish.

I try to get within +/- 0.01mm on diameters at home (Super 7 with mainly HSS tooling) whether the part really needs to be that accurate or not – more to try to get into an "acccurate" habit so that there is (maybe) more chance of getting an accurate part first time when it does matter. Same goes for surface finish – practice getting it good so that good is the norm. Frequently don't succeed on either count but, hopefully, regular practice will make for more reliable results !

Milling / shaping probably get within +/- 0.03mm – I seem to be able to get reliably closer than this a work on an XYZ turret mill with DRO & new cutters, so probably a combination of less rigid machinery, no DROs & less use of new cutters at home gives the worse result (FB2 clone mill & Boxford shaper).

Have not yet tried the Ingar RT612 surface grinder in anger, but used the same make/model at the last employment & could get as close to a desired size as I could measure – just took time & elbow grease !