How to use a round column mill

I have a mill that has a round column with a rectangular strip to keep alignment.

It also does not have a fine feed or depth stop on the Z axis.

So far I have used it with end mills and it seems to cut fine, but I have a couple of questions on how to use it for slots and boring.

I tried cutting a 8mm slot using a 2 flute slot cutter. When cutting vertically i.e. starting the slot, the head started violently vibrating side to side, but horizontally is fine.

I used the quill feed so dont have a good feed rate, but guess it was about 1mm/10s.

I found if I drilled a hole first, the vibration stopped so I guess it is due to the asymmetric forces from the different length cutting edges.

1. Is it normal for a slot drill to do this?
2. Am I expecting it to cut too fast vertically?
3. Should I use the quill or Z axis to give the vertical feed?
4. Is this just a limitation of the round column design and I should get a mill with a dovetail Z axis?

Thanks

Adrian

1. No it isn't normal, but on any mill play in the quill, bearings or work clamping, or a poorly ground cutter, will lead to vibration and the slot drill possibly cutting oversize during plunging, even with a centre hole

2. Feedrate seems way too slow although spindle speed isn't quoted. I normally plunge at about half the normal feedrate in deference to only one edge cutting all the way to the centre. Assuming a HSS cutter and steel workpiece I'd be running at 1000rpm and a plunge rate of 80mm/min

3. Personally I'd use Z, but I have a mill with dovetails on Z so that makes life easier

4. Not for me to say

It really comes down to machine mass and flexibility. On my vertical mill an 8mm cutter would be fine, but I have seen the same issues when using 20mm, or larger, slot drills.

Andrew

Round column mills don't usually have an alignment strip. They clamp the head securely and rely solely on the quill for Z axis. Whether yours can be used moving the Z axis depends upon the fit of the rectangular strip stopping any tendency for rotation. This could be verified using a dti when the head is free to move up and down to see if the head can be rotated on the column. More than 0.002" movement would be too much.

Had you clamped the head or were you thinking the 'alignment strip' would keep it steady? If you have what is known as a mill/drill then 100% you are meant to tighten those bolts even when just drilling.
Just because you can plunge a slot drill doesn't mean you shouldn't drill a hole first 90% of the time and save its end cutting capability for when there is no option.

Mill/drills are perfectly satisfactory for hobbyists on a budget making normal sized models. If your line of modelling needs a trailer to move it then you might need a bigger mill too.

Hi Adrian,

I see the mill in your photo album is a clone "type" of the Emco FB 2. As the Emco mill has a strip attached to the column to ensure alignment, I am presuming yours is the same.

To produce a slot I usually drill a hole 0.5 mm smaller at each end of the slot if it is not open ended. Then with the cutter inserted I lower the quill, and lock it. Then set the depth stop on the quill. The whole head is then lowered and the cutter brought into contact with the job. The down feed is then set to zero. Retract the quill and put a cut on using the down feed handwheel.

Lock the head to the column. Start the machine and at the one end of the slot feed the cutter down using the quill until it hits the stop. Machine the slot to the other end, (I usually set stops when doing slots), traverse back to the start. Repeat the above until the slot is to depth.

To get a really good slot use an undersize cutter first, and rough out the slot. Move off the centreline an equal amount to remove some, but not all of the material on the sides. The difference in the undersize cutter and the size of the slot minus 0.2 mm is my usual.

Move back onto the centreline and insert the correct size cutter. Again I set the quill stop as above. Then at each end plunge to depth. On the last plunge cut lock the quill and traverse to the other end of the slot and back.

It takes longer to write down than do, I hope this helps?

Regards

Gray,

I was running at 880 RPM.

The strip is not that large, I just had a check and when unlocked it had 0.015", I have nipped it up a bit and now have about 0.006". Oddly when it is locked I still have 0.004" play, not flexing, as the movement stays after I let go.

I will have to investigate further, but I could be flogging a dead horse, the manufacturer describes it as an educational mill/drill

Gray thanks for the identification, I had been wondering what it was a copy off. I had thought of using the quill end stop, but decided fully in would be more rigid. I will give the fully down method a go.

Bazlye I had the Z locked as I knew about the play on the strip.

Hi Adrian,

I may have misled you slightly. Only extend the quill sufficiently to do the slot in hand.

Regards

Gray,

Could we have more pictures of the mill? Possibly a name and there may be more info on the "lathes UK " site.

The mill is a ZX-16 sold by Engineers Tool Room in 2003 as a BMD-16 but still badged as a ZX-16. Till today I had not known it is a copy of a Emco FB2. Looking at the head, the casting is identical, and I have also seen a youtube video showing internal parts, they look the same as mine.

It is still sold by the OEM XYMC

Could the metal guide strip on the column be loose? Without a fine feed on the quill, the only way to move slowly in the Z axis is with the wheel at the rear. Are any adjustments possible to the fit, such as a vertical jib strip?

 In your first picture, behind the 11 on the rule is a plate which looks like it is a pointer. Can the column be rotated in the base? Is it tight?

Edited By old mart on 01/07/2019 20:10:22

I have 3 FB-2 mills and have no problem with any, within the limits of such a structure..

The key is to ensure the various adjustments are well taken care of. You will never mill as heavily with Z axis motion as you could with a dovetail column mill. Likewise, in X and Y, you need to lock the head on the column when taking heavy cuts.

In the first picture you can see the vertical head Gib - item 20. This must be really well snug in the slot, up against the vertical key. Also, the sequence of setting the screws is important

page 2 shows the gib again (item 5) and all the setup screws.

It is also very important to ensure the two hex screws in the column support ( the base part) are well tight to ensure the column cannot rotate.

If you cannot read the text on page one, PM me and I will scan the pages and send them via email...

Joe

Joe has it I think.

Time to do a very careful engineering assessment of the machine and verify that the copy is made to comparable tolerances to the original and works in exactly the same way. The Emco original is very much designed to be built to a price point and, inevitably has various inherent compromises in concept that are only acceptable if the machine is appropriately constructed.

I know from personal observation that, as Joe says, they can do good work when driven appropriately.

I had a ZX32 dovetail column mill from the same factory that was of fundamentally sound design with a few bloopers in construction leading to inconsistent results. Took about two years of shop language and persistent investigation after each "got it now" fix proved insufficient to finally sort it. Hafta say that some of the errors were hard to find because I never expected a machine could get out of the factory in such a state. Last one I found was an oversize slot in the X axis taper gib coupled to a bent adjuster screw with its head made on an angle so one side was thicker than the other. The fundamental machining was very good and of more than decent accuracy but clearly quality control of many smaller components and the overall assembly process was less than non-existent. I sort of imagine the assembly guys (& gals?) being given a box with a complete set of unchecked parts and being told to put it together with no excuses for parts that didn't fit properly. Always assuming that the line staff were trained to verify proper fit in the first place.

If mine was a typical example of the culture at that factory I'd be unsurprised to hear that you have similar issues. That said I'd be confident that the fundamental machining and alignments will be good so chasing out the issues will be worthwhile.

Clive

Joe, thanks for the info.

I did make some adjustments to the gib and the hex screws today. However I think after reading those instructions I will look at it again tomorrow.

I did initially have a problem with the column rotating when doing the vertical plunge. It shifted the head about 3mm which I could not move back without loosening the column. The side way forces from the slot drill plunge are really quite high, much higher than an endmill traversing. I have tightened the column and it is the vibration after that which I am asking about.

I have some more slots to cut tomorrow so I will see if the column adjustments have improved it.

Adrian

My first mill was even less rigid than that - with three axes of adjustment on round columns/arms. I always needed to set the vertical such that the head was hard up against the winding strip, before tightening, such that it was forced against the strip when milling forces were applied. Any chatter in the other way would/might cause movement.

It worked for me until the limitations were solved by buying a more ‘orthodox’ milling machine.... It did not cost me a great deal, money-wise, but was hard work getting a job done accurately. It was a steep learning curve at the time.

I wished, in hindsight, that I had bought a better machine in the first place. Isn’t hindsight marvellous!

As well as looking at the sharpness of your cutter I would drill the ends or ramp down into the slot rather than plunge cut.

A bench top machine of this size is probably a bit light to plunge straight in with a cutter of that size, I know my X3 would complain and I'd not be able to get anywhere near the feed rate suggested by others earlier. So best to tune it up as detailed above and then change your methods.

I am not sure I agree with all the deriding statements re a round column mill. It IS less rigid than a decent dovetail column, but the limitations are very easily endured IF the mechanical setup is properly adjusted, as for ANY dovetail arrangement. Any loose adjustment anywhere critical will show up on any type of mechanical arrangement. I have 3 Emco mills now for over 25 years and if you might care to take a look at my albums you may see a large variety of work having been successfully executed on them. One of the three has been converted to full CNC with ball screws, and has milled full 3D work, with CNC motion in Z, of course requiring that the head can move up and down freely, aligned only by the properly adjusted slide screws and the gib. Granted, I do not do the type of Heavy Steam Generation work such as Jason does, but milling 25mm deep dovetails on phosphor bronze, with a 75mm diameter dovetail cutter is a doddle.

So, Adrian, do not let the naysayers put you off! Unless there is fundamental poor mechanical workmanship in the fit of your mill's parts, correct setup will give you a machine that is a pleasure to use, within its size limitation.

Regarding the 8mm slot drill - repeat the test before doing ANY adjustments and when the head 'vibrates', try to see where the motion takes place, ie, is it the column itself rotating in the base, or the sliding head on the column.

If the base/column junction, snug up those two hex bolts in the side of the base and try again. If not the column, then fasten up the vertical slide clamp, maybe slightly over tight, and try again. It the problem is mostly gone, then you need to do those adjustments as in page 1 of the pics.

Note also that rigidity on these machine does get worse the higher the head is raised..

Joe

Irrespective of the type of Slide way, the "Column" on any bench mounted machine is a torque tube.

I have used Emco FB 2's for for nearly 40 years now and if treated with respect they can turn in a surprisingly good performance. I would not change my machine for anything else.

Correct adjustment of the slider on the column is the secret.

As regards Fine feeds, here is something I added some years ago .

The attachment was recently described in HSM.

Regards

Gray

I second that wholeheartedly! Really a very nice machine.

That fine autofeed is a superb mechanism Graham - very nice indeed.

Here's one of mine, with power feed on X and Z.

Did not know they came in Red and Grey!

Joe

Hello Joe,

Nice set-up, OH for a bigger workshop.

The Red and Grey machines were the last of the line. I think the decibel levels of the machines were getting close to the then latest regulations. Emco then went over to belt drive, one of the two machines available I think used a similar FB-2 head casting, this had variable feed. These came on a different base casting which I think was from the Orient.

Regards

Gray,