Do you really need 12.9? as they will be in compression I'm sure 8.8 ones will do

Cap heads work fine for me

Edited By JasonB on 03/09/2015 12:25:53

Suggest turn off the first two threads off the end of the bolt,leaving a plain diameter at just below core diameter ,repeated use of the bolt tends to swell the end of the bolt so when a bolt eventually requires replacement it cannot be unscrewed ,the plain portion may swell a bit but it still allows easy removal. Probably easier and cheaper to find and use 8.8 bolts and replace them a bit more often.

I got a batch of M6 and M5 8.8 stainless screws from Screwfix for my toolholders. They have a neat chamfer at the end so I don't have to worry about the swelling that eventually spoiled the M6 ones in my toolpost (admittedly after over a decade). they don't seem to be showing any signs of suffering distortion.

Last batch I bought had 'square' ends though, so it seems to be pot luck what you get.

Neil

For reference:

Fastener properties

Murray

Fairly ordinary bolts will be fine in this application as the overall forces aren't that high. Bolt up construction from standard plate and bar sections saves a ton of machining and is probably more accurate if you don't have a horizontal mill or shaper to hand. Main thing is to arrange top and bottom plates to be thick enough to prevent any bending when tool is bolted in firmly. Especially when post is removed. Bolt end mushrooming is a fact of life for this sort of thing so its important to remove the first couple of threads as advised by Bob and to regularly pull the bolts to clean up the end. Even the pro gear suffers. Got some Dicksons for £ very reasonable and had to file the mushrooms off about half the bolts in situ to get things good enough to use. Not a pleasant task! Allegedly a piece of 1/8 or so alloy between bolt ends and tool top both prevents mushrooming and gives a better grip at lower torque.

Square heads are less obstructive than hex so if you have a suitable tube spanner machine down the heads to suit. Mr Dickson makes the across flats dimension of his squares same as bolt diameter so, for M10, 3/8 A/F would do just fine. Same size as my T2 Dicksons. Especially if you don't have a suitable tube spanner as Dickson spanners can be purchased or female end of an inexpensive socket adapter would be a good start on making one.

Two way is easier and stiffer than four. Also narrower which can help when working between centres if the tailstock gets in the way. I've almost never loaded a four way with more than two tools so the simpler form doesn't seem a great disadvantage. If you can make more than one post and arrange matters so that they can quickly be interchanged with some sort of alignment gauge or indexing system. Sort of poor boys QC system.

I drew up, but never made, what looked to be a promising QC set up for this sort of thing. Centre stud was to be fairly large diameter and arranged to rotate. Toolholder was threaded in the middle for a large hollow bolt with a castellated end. Centre stud to be cross drilled in alignment with the castellations so a loose tommy bar could be pushed through both. Turning the tommy bar would rotate the stud and wind out the hollow bolt gripping the bar between the castellations and stud cross drilling to clamp the tool post down. Unwinding the hollow bolt a third of a turn or so would release the tommy bar so it could be withdrawn and the tool post lifted off. My plan was to so equip a SouthBend Heavy 10 but a Smart & Brown 1024 arrived at the right price with a Dickson tool post and starter kit (5) of holders so the project was abandoned.

Clive.

Edited By Clive Foster on 03/09/2015 16:13:57