Newbie problems milling steel

[Men IfrParticipant @menifr84251]

Hi to all. I just got an SPG 9512 basic milling machine. I also bought a cheap clamp set. The problem is the T nuts are too deep to fit the machine. I thought I know I will mill some material off the bottom. So with a new 10mm 4 flute cutter maybe 3 to 500rpm trying a full cut about 2mm deep and feeding in slowly on this manual machine did not seem to go well. It cut a bit of a slot but then seemed to need a lot of pressure and I started to get vibrations from the machine. I tried again but still no luck. I then tried to cut a 3mm wide by 3mm deep slot off the edge and again I’m putting a lot of pressure on the handwheel the machine is complaining and very little milling is happening. The workpiece looks very sloppy I think the cutter is now blunt. Any idea what went wrong? The cutter was a sherwood so should have been good. I have more cutters but am reluctant to try again for fear of ruining those quickly. Oh I wondered if the t nut would be hardened so I tried filing the edge and it files easily so I don’t think it’s hardened.

[Men IfrParticipant @menifr84251]

[mechman48Participant @mechman48]

You haven't got the 'X' axis locked up or the stops butting up against the table central stop block have you ?

George.

[Anonymous]

Posted by Men Ifr on 14/03/2016 20:50:42:

…….. and feeding in slowly …………….

Therein may be your problem. Cutters need to cut, if you feed too slowly they just rub, go blunt quickly and everything vibrates. For a 4 flute cutter at 500rpm you should be feeding at 100mm per minute or more. Also be aware that the T-nut is unlikely to be 'quality' steel so whatever you do may not result in a great finish.

Andrew

[HollowpointParticipant @hollowpoint]

Make sure you aren't running in reverse. Make sure everything is locked up and as rigid as possible. Take a smaller cut with a bigger cutter.

[Chris Evans 6Participant @chrisevans6]

Try a file on the tee nut, most seem to be hardened. Also reconsider cutting off the bottom as tee nuts are generally not tapped all the way through to save you bottoming a bolt/stud out on the table and straining/breaking the tee slot in the table.

[mark smith 20Participant @marksmith20]

I think you`ll find you`ll have to fiddle around with that machine before you get any decent results.

I`ve had the Warco version of it for around 10-12 years, as a first mill , i still have it even though i had hoped to have upgraded to something better by now.

I found going to tapered roller bearing in the head was a great improvement ,also added a belt drive,as i broke the gears twice on it.

It is not an awfully rigid machine and some fill the column with sand /epoxy mixture and add a plate between the base and the column to add mass and prevent it moving(which is ok if you don`t use or intend using the tilting column.)

[VicParticipant @vic]

I know it doesn't address your problem but I've never found shop bought T nuts to be a good fit so I've always made my own. Making them was the first job on the two mills I've had. The couple I did buy just get used as packing pieces these days!

[John HaineParticipant @johnhaine32865]

That's an X2 mill I think. 2mm DOC sounds a bit aggressive for that machine? How fast were you feeding?

Do you have a magnifying glass? Look at the tool edges in a good light – you'll see if they have been damaged.

You say you checked with a file so the steel doesn't sound hardened but I guess it might have a bad patch.

This machine doesn't have table stops so it can't be that.

How were you holding the cutter? Jacobs chuck or collet?

How were you holding the work? A quick alternative to proper tee nuts is a bit of MS bar that just fits in the base of the slot and can slide along, with a tapped hole. Most tee nuts have a hole right through but often the bottom end is burred over to prevent the stud bottoming against the base of the slot – do the same on this quick alternative for the same reason. But proper tee nuts are better.

What do you mean by a "sloppy" workpiece?

If the cutter is blunt then you'll have to try another one. Hold it in a collet. Try 0.5mm DOC, don't be shy with the feed but not silly either – you should be able to tell if it's happy, it will make a sort of "chuffing" sound.

[JasonBModerator @jasonb]

As Chris says the nuts may well be hardened, mine are lightly hardened and when I needed to machine two of them I used carbide insert tooling which coped OK. Also agree about cutting the bottom off, beter to take a bit of each side to make the T shallower and then reduce the top so it won't stick up above the table.

You have quite posibly blunted the cutter now so no amount of extra pressure or tweaking the machine will help.

[Neil WyattModerator @neilwyatt]

2mm should be fine on an X2. Making t-nuts on it I would do each side in one pass (but not in hardened steel!)

Files are very hard – they will mark most steel that has been hardened and tempered, if they skid across it usually means the steel is hardened and NOT tempered ('glass hard'.

Might be easier to take the bottom off the t-nuts using a bench sander or a grinder (you will need to find a safe way to hold them).

Use a centre punch or similar to distort the bottom threads so you don't have to worry about the stud coming right through.

Neil

 

Edited By Neil Wyatt on 15/03/2016 10:11:41

[steamdaveParticipant @steamdave]

Posted by Chris Evans 6 on 15/03/2016 09:12:30:

Try a file on the tee nut, most seem to be hardened. Also reconsider cutting off the bottom as tee nuts are generally not tapped all the way through to save you bottoming a bolt/stud out on the table and straining/breaking the tee slot in the table.

Not a problem because the last thread can be deformed easily.

Put a ball pein on the threaded hole and hit the other side with another hammer or for those who are cringing, use a steel ball larger than the hole instead of the ball pein. This damages the last thread to prevent the bolt bottoming.

Dave
The Emerald Isle

[Men IfrParticipant @menifr84251]

Thanks for all the replies – some answers:

[Men IfrParticipant @menifr84251]

Posted by mechman48 on 15/03/2016 08:51:53:

You haven't got the 'X' axis locked up or the stops butting up against the table central stop block have you ?

George.

No – workpiece was in the middle of the range of x/y adjustment – I locked Y and Z axis which does seem to help a bit and fed in via X.

[Men IfrParticipant @menifr84251]

Posted by Andrew Johnston on 15/03/2016 08:59:32:

Posted by Men Ifr on 14/03/2016 20:50:42:

…….. and feeding in slowly …………….

Therein may be your problem. Cutters need to cut, if you feed too slowly they just rub, go blunt quickly and everything vibrates. For a 4 flute cutter at 500rpm you should be feeding at 100mm per minute or more. Also be aware that the T-nut is unlikely to be 'quality' steel so whatever you do may not result in a great finish.

Andrew

I think this or the hardness of the material is the problem – I've since made a little spreadsheet based on calculations from an american site. If I feed in at 1 handwheel turn in 2 seconds = 3mm I should have 220rpm with a 4 flute 10mm cutter does that sound right?

As a beginner it's having the confidence to 'ram' the cutter into the work – particularly before I started out with the calculations above which show I need to slow the RPM a lot. If I picked a mid rpm on my machine e.g. 1000 I don't think I could turn the handwheels fast enough to meet the desired linear feed rate!

[Men IfrParticipant @menifr84251]

Posted by Hollowpoint on 15/03/2016 09:01:50:

Make sure you aren't running in reverse. Make sure everything is locked up and as rigid as possible. Take a smaller cut with a bigger cutter.

Not in reverse – I think feeding in too slow may have been the problem last time – so think I should be going faster – 10mm is my largest cutter…

[Men IfrParticipant @menifr84251]

Posted by Chris Evans 6 on 15/03/2016 09:12:30:

Try a file on the tee nut, most seem to be hardened. Also reconsider cutting off the bottom as tee nuts are generally not tapped all the way through to save you bottoming a bolt/stud out on the table and straining/breaking the tee slot in the table.

I did this on a corner – it filed easily but I'm wondering if there is something about this steel that is causing problems?

After the initial problems – with the same cutter I successfully cut the 'T' part of two T nuts – this time I was feeding a bit faster and using climb milling. After 4 more cuts then the mill was no longer cutting well – again taking excess pressure on the handwheel – vibration and squeeling from the workpiece/cutter. When I looked at this workpiece it was not cutting cleanly – more like pushing the metal out of the way.

[Men IfrParticipant @menifr84251]

Posted by John Haine on 15/03/2016 10:00:01:

That's an X2 mill I think. 2mm DOC sounds a bit aggressive for that machine? How fast were you feeding?

Do you have a magnifying glass? Look at the tool edges in a good light – you'll see if they have been damaged.

You say you checked with a file so the steel doesn't sound hardened but I guess it might have a bad patch.

This machine doesn't have table stops so it can't be that.

How were you holding the cutter? Jacobs chuck or collet?

What do you mean by a "sloppy" workpiece?

If the cutter is blunt then you'll have to try another one. Hold it in a collet. Try 0.5mm DOC, don't be shy with the feed but not silly either – you should be able to tell if it's happy, it will make a sort of "chuffing" sound.

I'll try a new tool – I have some chinese cutters now – reluctant to try another sherwood ££!.

I'll try a low DOC and feed in faster. I will also try some other steel first in case it is the material of the nuts.

So what if I try – some old mild steel – 0.5mm DOC 4 flute 5mm chinese cutter at 1200rpm and 1.5mm/sec feed speed?

I'll buy a magnifying glass to look at the old cutter.

[Men IfrParticipant @menifr84251]

Posted by JasonB on 15/03/2016 10:02:18:

As Chris says the nuts may well be hardened,

You have quite posibly blunted the cutter now so no amount of extra pressure or tweaking the machine will help.

Should I give up on these and continue to use the angle grinder for fear of damaging more cutters?

[HollowpointParticipant @hollowpoint]

You might as well go ahead and make some t-nuts from a grade of steel you know. It will give you an idea if you are doing things right or not and save you some cutters. Quickest way is to make a long length of t and then just chop it up.

[Neil WyattModerator @neilwyatt]

Tubal Cain used to say – if cutters struggle reduce depth of cut, but keep up the feedrate.

Some neat cutting oil applied by brush will help ease cutting and prolong tool life.

neil

[Chris Evans 6Participant @chrisevans6]

You say you ran a file across a corner, even fairly hard steel will cut like that. Run the file flat across a face to see if it skids. By the way where are you based ? Someone may be close enough to help/advise you. Chris.

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