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Milling - What am I doing wrong

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petro1head03/03/2017 17:26:49
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540 forum posts
99 photos

All the gear and no idea

Got my new mill and busy making some T nuts

One side cuts fine but the other is tapering off the job

20170303_170439_001.jpg

untitled.jpg

The work is flat against the bed

So any idea why what I am doing wrong?

Martin King 203/03/2017 17:51:09
530 forum posts
167 photos

Look up 'climb milling' that is whats wrong I am pretty sure.

The bottom cut is correct but the top one you must go the other direction to avoid climb.

You must always feed against the rotation of the cutter, same as a woodworking router.

Learnt this the hard way myself!

Martin

Involute Curve03/03/2017 17:51:52
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318 forum posts
84 photos

Looks to me like the cutter is blunt, this could be causing the cutter to get pushed up into the collet or push the quil up, also you should not really be climb milling as you depict on the top part of your drawing!, although with that amount of stepover you will probably get away with it.

HTH

Shaun

Edited By Involute Curve on 03/03/2017 17:52:21

Toby03/03/2017 17:52:06
117 forum posts
17 photos

quill or z-axis not locked well enough?

stephen goodbody03/03/2017 17:54:09
34 forum posts
29 photos

I suspect that the workpiece is bowing due to internal stress relief, a common problem with bright mild steel due to the way it's manufactured (rolling). As you remove metal from one long surface there will then be an imbalance in the material's internal stresses which causes the material to bend.

The easiest way to overcome this is to remove most of the metal from opposite sides of the workpiece but leave some remaining on both sides - "roughing". You will likely still have a slightly bowed or a slightly tapered result at the end of the roughing cuts. Then remove the remainder on each side to finished dimensions.

The alternative is to heat soak the steel at high temperature (cherry red, if memory serves) for about 1 hour per inch of thickness and then let it cool gently to room temperature. This is known as "stress relieving".

Good luck,

Steve

 

Edited By stephen goodbody on 03/03/2017 17:54:45

Edited By stephen goodbody on 03/03/2017 17:55:23

Edited By stephen goodbody on 03/03/2017 17:55:53

Toby03/03/2017 17:58:06
117 forum posts
17 photos

If the diagram is the top view of the piece surly the one that is tapering up is the one that is NOT climb milling (ie the "bottom" one?

Stephen: surely if the workpiece was bowing that much you would see it? There looks to be a few mm taper on the cut but the bottom of the workpiece is still flat on the table?

Just curious btw, I don't even own a mill!

petro1head03/03/2017 18:07:27
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540 forum posts
99 photos

Grrr, its a bugger you can't edit posts after a period of time.

I have redone the drawing for clarification

untitled.jpg

Hi Toby, yet its the bottom bit, hence why I redid the drawing

I will also check quill movement, Z azis is rock steady

 

 

Edited By petro1head on 03/03/2017 18:12:10

Neil Wyatt03/03/2017 18:14:06
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Cutter is moving up into the chuck. Better than when it goes the other way.

What type of toolholding chuck are you using?

Neil

Mike Poole03/03/2017 18:14:57
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1546 forum posts
41 photos

It is good practice to lock all axes apart from the one feeding, what type of holder are you using to hold the cutter?

Mike

PaulR03/03/2017 18:17:32
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123 forum posts
21 photos

Mill table and head not perpendicular seems the obvious one to me - does it happen on everything? What if you turn the work-piece through 90 degrees?

IanT03/03/2017 18:19:37
1168 forum posts
118 photos

So the "good" side was the side you were climb milling on P1H - so that doesn't seem to be the problem here.

Basically, something seems to be moving for some reason. If the taper was in the other direction, I would suggest that the tool is being pulled out of the collet - but this seems to be the other way around. Even so, what kind of tool holder is being used? (not shown in photo) - as either the tool is moving in it or the spindle/quill is being pushed upwards l have to assume. So two things to find out - where is the tool "movement" and why is it happening.

What does the tool look like now and what feed/speed were you using when this happened?

Suspect blunt tool and collet not it holding tight enough...

Regards,

IanT

JasonB03/03/2017 18:19:48
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13710 forum posts
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As Neil says tool is riding up into the chuck/collet. Not helped by being a bit blunt.

Edited By JasonB on 03/03/2017 18:21:16

petro1head03/03/2017 18:20:03
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540 forum posts
99 photos

Posted by PaulR on 03/03/2017 18:17:32:

Mill table and head not perpendicular seems the obvious one to me - does it happen on everything? What if you turn the work-piece through 90 degrees?

I did wonder however used an acurate piece of metal and set the tool just kissing it at one end of the table the moved table to other end and tool still kissing the metal

Edited By petro1head on 03/03/2017 18:20:27

Edited By petro1head on 03/03/2017 18:21:57

petro1head03/03/2017 18:29:51
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540 forum posts
99 photos

I am using these collets - **LINK** which go straight into the spindle and the supplied draw bar.

Will check the tool however its brand new from Arc, HSS type. Spped was about 950rpm as per the chart I got off this forum. Feed, dont know Feet Per Min but not fast . I was take a .5mm cut. (when everthing is working fine could I take a deaper cut?)

Being logical I would say either the tool is moving in the collet or the quill is moving. If, and it could well be, the tool was blunt I am sure I would be able to tell and it would still try to cut.

BTW Thanks for you help and interest in my problem

Peter Tucker03/03/2017 18:31:36
172 forum posts

Edited out as already posted and answered while I was typing.

Peter.

Edited By Peter Tucker on 03/03/2017 18:34:18

ASF03/03/2017 18:32:10
125 forum posts
12 photos

I suggest you lock the head to the vertical dovetail(two levers on side) and the quill lever on left by quill.

Also lock the Y axis when milling on the X axis

I have a similar mill and everything has to be tight.

The milling cutter is dull and you need to learn to mill conventionally

All part of the fun of learning :D

petro1head03/03/2017 18:44:25
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540 forum posts
99 photos

Ok, when back in the hut to have a fresh look. Places the workpience on the table and wound down the head until the tool just touched the work. Then wound down the head some more to see if anything was moving and YES the handle for the quill was rotating. So I think thats the problem, I should have locked the quill Doooh!

So thats to you guys I have learned something and will lock everthing aexcept the moving axis.

ASF, what do you mean the cutter is dull? This is the cutter I am using - **LINK** At the time of buying I did wonder if I should have splashed out and bought Carbide but they were 3 x the price?

Edited By petro1head on 03/03/2017 18:45:26

Neil Wyatt03/03/2017 18:52:02
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14714 forum posts
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72 articles

Everything is lined up OK, and climb milling isn't the problem as the climb milled side has come out OK (assuming the diagram is right).

If you are using R8, then (1) they need to be done up very tight and (2) the cutter has to be the same size as the collet (unlike ER collets R8 won't work with undersize shanks).

You also need to be sure that both the head and the quill are locked in place.

I suggest marking the position of head, quill and tool, then taking another trial cut to see what is actually moving.

People are warning against climb milling, but it very much depends on how rigid you mill is and how tight your slides are and backlash is controlled. I climb mill on my wee X2.

There is actually more vibration with conventional milling when the mill is set up right, which could be the cause of the movement. How 'happy' did the mill sound and feel when you were taking the cuts?

Neil

ASF03/03/2017 18:52:02
125 forum posts
12 photos

I mentioned the cutter being dull because rather than a clean cut, the picture shows a rather messy burr as the cutter exits the workpiece. Inspect the corners of the endmill they should be very sharp. Cut (scratch) your nail sharp I would say. I am in the process of making a power feed for mine and a test today of a 12mm cutter (cutting full width) cutting 1mm depth was uneventful in mild steel

stephen goodbody03/03/2017 18:53:20
34 forum posts
29 photos

Ah - the revised drawing make things clearer. Ignore my earlier post about the workpiece bowing, that's not causing the problem here.

I agree with the other folks, it looks like the cutter's shifting or the table's shifting, likely because the cutter has blunted. As an attempt to provide suggestions (and no criticism intended), the following can really shorten the life of a tool:

- Removing too much metal in one pass

- Feed rate too fast

- Wrong cutter speed

- Lack of lubricant / coolant (squirt soluble oil at the cutting edges from a squeeze bottle or oil can - little and often)

- Tool quality (price is a good indicator of tool quality and life expectancy)

Good luck.

Steve

 

Edited By stephen goodbody on 03/03/2017 18:55:00

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