milling qestion

[mick70Participant @mick70]

couple of basic qs as still learning milling.

prob got total of 3hrs in on milling.

had to slot some brackets last night at work and needed to be dead central as between bolt holes.

easy with dro but if no dro could it be done by marking it out and using say a center drill to line it up then move piece to one side making sure not to move front or backwards and fit cutter then mill it?

also was using two flute slot cutter can i mill on return as well as forward?

i was just taking table back to start then starting again with cut,

ta

[mick70Participant @mick70]

[Anonymous]

I'd mark out the ends of slot using traditional techniques and the drill all the way through using the mill. Change to a slotdrill and mill the slot to full depth, stopping slightly short of the ends of the slot. On the last pass I'd take the slotdrill to the ends.

With any cutter, irrespective of the number of flutes, as long as you're cutting a full width slot it makes no difference which way you feed. So yes, you can mill in both directions.

Andrew

[Martin ConnellyParticipant @martinconnelly55370]

If marked out you can stick a drawing pin to the cutter with a bit of blu-tac or double sided tape or plasticene type materials. Run slow so as not to fling the pin off but fast enough to allow the mark one eyeball to figure the centre of the circle the point moves in and use that to centralize over the line. If the pin is too far off centre then reposition it a little to get it nearer the centre line, it does not have to be perfect.

You really should be supplied with a mechanical edge finder as a minimum extra bit of tooling. They are cheap but work well. Arc sell a selection for example but they are readily available from lots of suppliers. Youtube has a lot of how to use videos showing them being used. A wiggler works similarly and often the point in a wiggler set can be used more easily than an edge finder point.

Martin C

[not done it yetParticipant @notdoneityet]

Every job needs thinking about. Are these brackets held in the vise? In a jig? Clamped to the bed?

Before dro’s, marking out and centre punching was more common. Use of manual scales on the feed handles was the usual for slot length, taking into account any backlash as appropriate.

Makes no difference which way you cut if it is a slot – unless widening it.

Dependent on job, you could pilot hole and follow through with any end mill and just side mill (depends on thickness and cutter size, of course).

Sometimes better to chain drill and clean up the slot sides with an end mill. I use whatever cutter I think is appropriate to the job. Wearing out the sides of a cutter is, to me, often better than wearing out the ends!

Depending on the precision of the job and the precision of your machine, it may be better to mill only in one direction.

Most jobs I do don’t require absolute accuracy (often the amount of clearance is not critical).

Jobs with a 25mm wide slot maybe don’t need a 25mm milling cutter. Really narrow ones may be better cut to size in one go, but with shallow cuts.

Like I said earlier, it depends on the job. If you are not relying on it as your income, who cares if you make extra cuts as long as you get the job done. Is this a work job or a hobby job? Not sure from your post.

Edited to say t’others key in faster than me!

Edited By not done it yet on 13/07/2018 15:52:14

[TrevorhParticipant @trevorh]

The easy way is to drill the first hole at one end of the slot making sure the table is locked in position then fit an end stop, move to the other end of the slot and repeat

now you can change over to the slot mill and just traverse between the stops

[JonParticipant @jon]

Marking outs only as good as your eye, certainly if centre punching plus then its only as good as the position put the punch then hit. Will look different in various lighting change the angle you will notice then.

Easy way out pick up off the two holes just touch inner edge with a cutter if dont have any other means. Zero hand wheel dial then count the revs or distance and do same again to other hole. Split the difference.

Prefer 3, 4, 5 or 6 flutes for everything less torqueing off using 2 flute for slots if at all any. Can go like an S shape!
Can drill with milling cutters i do it every day but need to be centre cutting. If slots not through may pay to drill a smaller hole at or nea end of the slot, aids debris escape plus can them mill the opposite direction without having to feed it all the way back doing nothing.

Prepare to make mistakes, weve all been there no shame.

[Tim StevensParticipant @timstevens64731]

If your mill is a hobby type (not a solid heavy duty industrial model) then it is likely that a slot drill will be pulled over as it cuts*, so the edge of the slot isn't quite where you hoped. To cater for this action, use a smaller size of cutter (eg 6mm for an 8mm slot) and make the first cut down the centre line. Then as you remove the last bit, the pull of the tool will be less, and you will find it easier to cut to your intended line. It takes longer, but it works.

* This is because the front edge of the cutter is cutting all the way across one way, pulling the cutter towards the side where the cutting edge advances into the work. With an existing central slot, the pull is still there, but only 1mm is cutting, rather than 8, so much easier to manage.

And do have a practice on scrap of the material of the job, using the intended tool, to see how much extra is cut away.

Cheers, Tim

[Anonymous]

Posted by Tim Stevens on 13/07/2018 20:31:22:

If your mill is a hobby type (not a solid heavy duty industrial model) then it is likely that a slot drill will be pulled over as it cuts*, so the edge of the slot isn't quite where you hoped.

I've never used a hobby type mill, but I don't see why a slotdrill should cut wide on one. When the cutting edge reaches the widest point the edge will rub to start with, and the cutting edge will tend to be pushed away from the widest point of the slot. As the edge continues to rotate eventually the edge will start to cut instead of rub. But at that point the edge will be past the maximum sideways excursion, so even if it tends to pull the cutter towards the existing edge it won't cut wide.

Now I grant you I have a Bridgeport, but that isn't the most rigid of machines, and it's well worn. But slots cut full depth in one pass are within a thou on width, as measured with gauge blocks. At least some of that error is due to tolerances on the cutter itself.

Andrew

[HopperParticipant @hopper]

Posted by mick70 on 13/07/2018 15:01:37:…

easy with dro but if no dro could it be done by marking it out …

Back when only spaceships had DROs we just did things the same way as now but used the graduated dials on the handwheels as our readout. Backlash was not an issue if you always moved the table in the same direction, backing off past the zone of backlash and re-approaching the job from the same direction if necessary. Even with a worn leadscrew, error is so infinitesimally small as to be way more accurate than marking out and centre punching etc.

Why does using handwheel graduations seem to have become impossible to do these days?

[not done it yetParticipant @notdoneityet]

Hopper,

Ithink it is the backlash issue that slows people down or introduces inaccuracies. Finding the centre line is not quite as easy as returning to a start position as you described above.

For finding the centre of a bar, I used to rely on my odd-leg scriber, and a dot punch – as that was near enough for most jobs I used my mill for.

That eventually developed to using of an edge finder. Once the machine backlash was known, it was not a problem – even though my first machine had quite a lot!

[JasonBModerator @jasonb]

You don't even need to worry about backlash if you measure the amount of metal between the two holes, touch off on the inside edge of one hole and then keep turning the handwheel in the same direction for half the distance + half dia of what you touch off with be it a bit of ground bar, tool or edgefinder.

You can also put a plug in on of the holes which would allow you to touch off on the same side of both thus keeping the handwheel direction the same, then just go back beyond the mid point and wind into the required setting.

I've not found 2-flute cutters to go oversize on my hobby machine, at least not to an extent that I can measure, 4-flute will do it though.

Edited By JasonB on 14/07/2018 07:28:21

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