High tensile M6 bolts

[nevilletParticipant @nevillet]

Hi all,

I’ve recently taken delivery of a small Sieg SX2PG mill that came supplied with a clamping kit.

I’m assuming that the supplied black M6 studding and parts are made from high tensile steel.

I now want to make some bespoke clamps and studs.

Can anyone suggest what kind of studding (or long bolts that can be cut down) would be suitable?

Also what kind of steel section (possibly 25x10mm) would be suitable for the lever part of the clamp that I could machine a slot in?

Also I don’t want to wreck my new mill & cutters trying to fabricate these parts.

Any thoughts?

Many thanks.

[nevillet]

On 10 April 2025 at 09:39 nevillet Said:

[…] I’m assuming that the supplied black M6 studding and parts are made from high tensile steel.

[…]

Any thoughts?

 

1. Be wary of making assumptions.

2. Unbrako branded screws are a reliable source of high-tensile material.

MichaelG.

.

Ref. https://unbrako.com/

[JasonBModerator @jasonb]

If you are getting to the point of worrying about the tensile strength of your fixings then you are applying too much tightening force and that will risk damage to the machine such as the tee slots.

Mild steel will do which is around the 4.6 or 4.8 grade and if you really want HT then 8.8 will be more than adequate. Beware cutting the head off bolts and rethreading the end as they may be rolled threads which means the plain shank is undersize for threading with a die.

Plain Mild steel will do your clamps so EN3 will do and can be machined easily enough. The clamps I mostly use with my M6 fixings are 20 x 5 section.

[bernard towersParticipant @bernardtowers37738]

I agree with Jason if you need to have things that tight that you need HT bolts your clamping needs rearranging, blunt cutters etc.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I totally agree with what JasonB has said. If you use any that are higher than 8.8, don’t get carried away with the spanner, and a stumpy spanner will do in most cases anyway, but I wouldn’t go to the bother of making studs per se, as I just use threaded rod, and if making T-nuts, don’t put a full thread through them, or you can stake the underside to stop your studs screwing through them.

Regards Nick.

[duncan webster 1Participant @duncanwebster1]

I use M6 allthread, never had any problems, but then I’m a rough so and so

[JasonBModerator @jasonb]

That must make two of us, some random bits of unknown studding from my box of M6 “bits” which were just scrap from something else. The longer bolts are all un marked only the shorter screws are 8.8 but they were free not bought for their properties. So no real need to spend money on HT and certainly no need for name brand premium prices for this use.

Clamps 20×5 and 1/2 x 1/4, as I use them for silver soldered fabrications as well they are a bit rusty but also well annealed/stress relieved but still don’t bend under clamping loads unless I get silly.

[noel shelleyParticipant @noelshelley55608]

I’m with the rest ! be cautious of jacking a T nut up and bursting the slot, it can spoil both a nice day and your mill. Good Luck . Noel.

[nevilletParticipant @nevillet]

Many thanks for all your help and advise.

I have some M6 stainless studding which I guess will be fine and I fully take your points about over tightning.

I’ve found some L section (50x50x3.2mm) which might do the job for the hold down clamps.

I’ll put up some pictures..

[bernard towersParticipant @bernardtowers37738]

Im with you there Noel, I very often fit my studs to table with a large washer and nut to spread the load over a greater area.

[HOWARDTParticipant @howardt]

one of the things to prevent over torquing is use a standard spanner, the length of the spanner reduces the chance of stripping threads.  Also if parts are moving under cutting forces put the part in a nest, ie place the part against stops on the sides to which the part is moving or can move.  Or if you have holes in the part locate the part by a couple of holes.  I dont know what’s out there these days but have a look at jig and fixture reference books for ideas on holding different shaped parts.

[nevilletParticipant @nevillet]

Please bear in mind this is my first attempt at milling…

I cut the steel down using an angle grinder then tried to end faces parallel on the mill.

Then I cut 3x M9 holes with an HSS drill bit.

Then using the mill, tried to join up the holes to make a slot using a 9mm cutter.

I was a bit reticent of trying to do a plunge cut with the cutter hence the drilled holes.
The cutter in question was

I now realize that the slot is probably not needed and a midpoint hole would do the job.

If I was going to cut another slot it would be narrower, maybe 7mm.

Using a stubby 10mm spanner, I can feel the steel starting to deform as I tighten, so thicker L section steel required?

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, stainless steel is fine, but if you use stainless steel nuts with them, make sure they are well oiled, as stainless on stainless will quite easily gall and then you will not be able to remove the nut. For clamping, using stainless steel thread, it is better to use ordinary steel nuts, as these are less likely to gall, even when used dry.

One other thing is you should get your clamping bolt as close as possible to the item you are clamping down. Your clamp with the slot that you have made, is too thin for the length of the slot, and you would’ve been better to have just used holes.

Regards Nick.

[John HinkleyParticipant @johnhinkley26699]

Neville,

You may well find that you’ll get better results forming a slot with a dedicated slot milling cutter with, say, two flutes, rather than the four-flute version shown in your photo. It would obviate the need to drill a series of holes to be joined up later.  Often, the slot is formed undersize in width and widened to finished size afterwards, depending on the accuracy the job requires.

John

 

[nevilletParticipant @nevillet]

Here’s V2.

No pilot holes this time and using the 6mm 4-flute cutter I milled the slots in 5m passes.
The slots ended up being around 6.15mm.

I’ve also got a 6mm 3-flute cutter (ARC 060-283-05006) which I’ll use on the next one.

With skinnier slots and a wider body overall it should be more ridged..

[nevilletParticipant @nevillet]

Job done.

2 of 2 made.

Many thanks for all your help,

It’s much appreciated.

[Michael GilliganParticipant @michaelgilligan61133]

That looks tidy

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

There’s a risk the sharp edge of the clamp will damage the table.  Particularly as the tables of these mills are often unhardened – test  with a file.

 

Easy fix, reduce the pressure by putting a strip of metal, say 12mm wide, between the edge and the table.  Almost any metal will do.

Dave

[Clive Brown 1Participant @clivebrown1]

I would slightly alter the slot length aad washer diameters to get the studding as close as practicable to the object being clamped. In this case the vice. This ensures that the clamping force is being exerted mainly where it’s wanted. It also has the secondary benefit of reducing the force that could damage the table, as per SOD’s remark.

Small point but why not?

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