drill / mill table load

[nigel daleParticipant @nigeldale57578]

Hi All

I have a Fobco column drill ( floor standing model )with threaded nose cone that I propose to try doing some milling with. I have a very nice XY table which weighs in at around 40kg. Is that too much to sit on the drill table without doing any long term harm ? I imagine that the downward force when drilling exceeds this loading but would the column take this much load long term without any distortion ? Your comments would be appreciated.

[nigel daleParticipant @nigeldale57578]

max safe loading

[Mike PooleParticipant @mikepoole82104]

I doubt that the weight of the xy table will be a problem but you could put an indicator on it to see how much it moves when the table is loaded on. I think you may run into trouble with a means to hold the cutter reliably. The screw on type nose may get round the morse taper problem but if you intend to use a drill chuck to hold the cutter you may find it will not perform as well as a dedicated milling chuck and the cutter may move. As you have what you need then give it a go but I would be prepared for things to go wrong.

Mike

[not done it yetParticipant @notdoneityet]

Acro prop, or two, under?

[jann westParticipant @jannwest71382]

hehe … as much as the acroprop is a bit amusing, a small bottle jack with an appropriate length of pipe as a spacer (and a spirit level on the drill table) is a reasonable solution.

I would imagine that 40KG + workpiece + downward pressure is pushing the drill beyond its intended design cone (and I do own one) … You'll notice that the one on lathes.co.uk mounts the xy table on the base, where this is not a problem.

[SillyOldDufferModerator @sillyoldduffer]

Since the dawn of time, all advice I've ever seen has agreed solidly it's a bad idea to use a drill as a mill. And my one attempt at light milling in a pillar drill was a hopeless failure: vibration, inaccuracy, work moving under pressure, cutter coming loose, you name it.

Although mills and pillar drills look similar, their design is different. A milling machine:

• Has bearings and structure designed to resist strong sideways forces; drills don't
• Uses collets to grip the cutter rather than a chuck. A drill chuck is designed to push drills down, not to move cutters sideways. As they don't grip nearly as well as a collet, it's likely that a milling cutter will come loose.
• Uses a drawbar to hold tooling very firmly in the spindle; a drill has no such provision
• Has good provision for holding work solidly in position, not just a heavy slotted table, but locking clamps on all three axes.

My admittedly cheapo pillar drill is very bendy compared with my milling machine. Putting a DTI on the drill shows that it flexes and twists much more easily than you might expect in every direction other than up-down. You might try testing how much your Fobco flexes by heaving on it with a DTI attached before spending time on an expensive experiment.

But hey, please give it a go and let us know how you get on. It's not unknown for the collective wisdom of the ages to be wrong! In this case though, I'm afraid it's spot on.

Dave

[Clive FosterParticipant @clivefoster55965]

Although milling in an ordinary pillar drill is generally considered an unsatisfactory, even dangerous process, the Fobco is designed to be capable of light milling.

Fobco bottom spindle bearings are an pre-loaded angular contact pair of the style common in milling machines and are well up to the loads. The screw on cap spindle is intended to take morse taper collets of similar style to those used by Myford giving both good grip on the cutters and minimal projection.

Its not proper milling machine tho'. Performance is limited by the relatively small diameter quill which is inevitably less stiff than that on a proper milling machine. The fine downed arrangement is little rudimentary and not as positive as that on a proper mill. I would hesitate to use one without the fine downed for milling duties. Although things will certainly work from the cutting perspective getting exactly the right depth of cut may be challenging.

It is what it is and certainly well up to handle appropriate sized milling cutters. In my view its best suited for jobs like spot facing, smoothing out faces and cutting flat bottomed slots or recesses where decent surface geometry and finish are the aim rather than precise depths. The pillar drill style depth stop is entirely adequate for jobs where 10 or 20 thou absolute error is fine. You'd need to work much harder to do significantly better on a routine basis. No substitute for fine downfeed really.

Were I intending to try more serious milling work I'd look into arranging a much more positive depth stop with integrated "display on a stick" depth reading device. I'd be unsurprised to discover that thou' or better depth accuracies could be achieved by working to a stop in this manner. Certainly the essentially similar arrangement I made for my square column Chester Lux style mill could achieve such accuracy. Making an accurate vertical cut on a Fobco would probably only be possible by setting the depth stop first. I found such work was doable but something of a faff on my mill but I'll not claim that my particular depth stop and readout system was the best that could be produced but it worked adequately with a fine down feed.

Extra table support is essential.  Bottle jacks can creep and ordinary automotive scissors units are flimsy.  Old style bevel gear driven vertical screw jack would probably be the most secure.  Come up fairly regular on E-Bay or boot fairs.  Ideally you'd want a finer screw thread.

Clive

Edited By Clive Foster on 12/04/2018 10:05:14

[OldironParticipant @oldiron]

I sold my Fobco Star bench model off a few years ago when I bought a 2nd larger milling machine and needed the space. Before that I did look into using it as a light milling machine. I dropped that idea when I checked the quill and found 0.005" side play. The table also had some vertical & horizontal wiggle in it. At the time lathes.co.uk were selling a replacement quill with upgraded bearing and a 2MT nose. It was if I remember about 1/2 the price of a used minimill so I went that route instead although I bought new. I would think that the 40Kg table as nice as it is, might be is a tad on the heavy side for the Fobco table even if you have the extra locking ring below it on the vertical shaft. I reckon adjusting that up & down would be difficult.

regards

[VicParticipant @vic]

Posted by SillyOldDuffer on 12/04/2018 09:10:39:

Since the dawn of time, all advice I've ever seen has agreed solidly it's a bad idea to use a drill as a mill. And my one attempt at light milling in a pillar drill was a hopeless failure: vibration, inaccuracy, work moving under pressure, cutter coming loose, you name it.

Dave

Been there, done that, same result!

[not done it yetParticipant @notdoneityet]

Vic,

I used to use a machine like that – only it was a milling machine! There is a wide spectrum in capability. It did for me, for a few years, but I would not use one like that now.

The acro suggestion was just that – a quick suggestion – but many machines have been supplied with supports from table to the base, over the years. Particularly thinking big shapers here.

[nigel daleParticipant @nigeldale57578]

Thanks very much indeed for your various replies. Not massively encouraging but I shall hold onto your response Clive. I will have to experiment and see how thinks " evolve " . Sadly I do not have the luxury of a spacious workshop so one machine has to suffice. A prop of some sort may be a wise precaution which will effectively fix the table but moving the drill head will probably be an easier option anyway. Thanks again one and all.

Nigel

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