Faceplate mounting on a horizontal mill (Centec 2a)

[Henry BainbridgeParticipant @henrybainbridge40560]

I just saw this video: https://www.youtube.com/watch?v=0znLGi_fCcg and wanted to do something similar.

I need to turn the edges and face off a 14″ alu turntable platter. I don’t have a lathe big enough but I have a Centec 2a with a 30 INT taper.

How advisable is this, and if not ill-advised, what would be the best way to go about it? Anything I should bear in mind?

[DC31kParticipant @dc31k]

Many a horizontal mill has been used as a lathe in the past. Nothing wrong with the concept when used with care.

Will 7″ fit between the spindle centre and the top of the Y-axis dovetail on the knee with the knee at its lowest?

What is the slowest speed at which the mill will turn? Does that give a slow enough surface speed at 14″ diameter?

It will need a good riser block to bring the cutting tool up to centre height.

Having the 30 taper will in some respects be a better starting place than the other option of 2 Morse (larger, stiffer).

Having the 30 taper will in some respects be a more difficult starting place than the other option of a 2 Morse. A 2 Morse to Myford thread arbor is cheap and allows easy mounting of pre-existing chuck or faceplate.

It is difficult to find the equivalent of a soft, blank arbor in 30 taper. For a one off, maybe put an ER40 chuck in the mill taper and then make a straight-shank adaptor suitable for your chosen faceplate or chuck.

You might have to make a 30 taper shaft and weld a round plate to it to make a faceplate. Truing it up will be a test run before you bolt the aluminium to it for the real job.

If you find a 30 taper to D1-3 adaptor on your travels, please pick one up for me.

If the mill-as-lathe does not work out, it might be possible to use a horizontal rotary table powered by a cordless drill and a flycutter in the vertical head for facing (the finished surface would look as if it had been Blanchard ground). The difficulty would be the 3 1/2″ radius (7″ diameter) that the flycutter would need to sweep without hitting the column of the mill.

[Nigel Graham 2Participant @nigelgraham2]

Since the tool would need be high enough to reach the work centre while the knee is still below the rim of the disc, do you have a rear tool-post for your lathe? If so, that may solve the problem provided you can fit it to the Centec table satisfactorily. (That for the Myford lathe, for example, has a tenon on its base, which may not fit a Centec Tee-slot.)

Alternatively, make a tool-holder by milling a channel along a steel, cast-iron or indeed aluminium-alloy block provided with appropriate tapped holes; one set for screws securing the tool in the channel, the others for fastening the block to an angle-plate.

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Regarding using a fly-cutter with the plate on a rotary-table, I would take this in two or more stages by moving the table longitudinally between complete RT rotations, so the cutter does not need a full 7″ diameter sweep. That is a massive sweep for a fly-cutter on a small machine, would put considerable strain on it, and could give poor results.

Power-driving the rotary-table is not essential but would give a constant feed-rate hard to achieve by hand, giving a much better surface finish. Would a cordless drill in direct drive be too fast? I have not tried it, but it may work on a screwdriver setting.

The RT need not be centred to the spindle for facing (as it would for milling any additional features of course) as long as the innermost area is still swept by the cutter.

 

[Henry BainbridgeParticipant @henrybainbridge40560]

That’s great news, thanks! The plan is to mount a spare Dickson tool post on a 5” riser, giving just over 7.5” between horizontal spindle centre and top of knee dovetail. The riser will have a central bore for some threaded bar to both keep the riser in place with a T nut on the bottom end and hold the tool post down with the usual hex nut at the top.

For extra stability a .2 inch deep tenon will be machined in the base which can slide along the T slot of the table as suggested. I do have a rear tool post which I considered using but it’s a bit too short and I need something a little more versatile for some features I am planning.

I have an old faceplate that doesn’t fit my lathe so I have rebored it and cut a new internal thread to fit an existing threaded 30 INT shank. I will fix the platter to the faceplate with some bolts threaded straight through from the back, ensuring they don’t go all the way through of course, as I need to face the entire surface in one pass ideally.

I think the slowest the Centec will do is 40rpm, so I will start there. Hopefully I can find a speed that will work well across all 7 inches, as I can’t change gear on the fly. I have powered table feed on the x axis though, so hopefully it should look pretty neat.

This is for a vinyl lathe project so accuracy is important. If there is too much runout I might have to go the RT route but I will cross that bridge if I come to it. Thanks again!

 

[Nigel Graham 2]

On Nigel Graham 2 Said:

Since the tool would need be high enough to reach the work centre

Thanks for that observation.

For posterity and for tohers we should perhaps note that for more limited utility (e.g. just turning the OD and not facing to the centre) the tool could be mounted so its shank is vertical (so adjusting the X-axis would adjust the centre ‘height’).

It could in principle be mounted at any angle to the table of the mill, just so long as it points towards the centre of the work. Vertical and horizontal just make putting on the cut considerably easier.

I think you’d have to draw a picture when considering the swept diameter of the flycutter. You’d need to draw the column of the mill and draw the vertical spindle centreline in relation to that. Then you would need to put a 14″ diameter circle on the drawing such that it did not touch the column. That would tell you how big the cutter would need to be to reach all the circle.

My gut feeling is that the vertical spindle of a Centec head is not 3 1/2″ from the face of the column. On a ram-type (Bridgeport) milling machine, the problem is greatly reduced.

[Henry Bainbridge]

On Henry Bainbridge Said:

an existing threaded 30 INT shank.

Thanks for that. The obvious off-the-shelf candidate for that would be a 30 taper threaded shank for a boring head (I think they are 1 1/2″ – 18).

How much inertia will the setup have? Alternatively, how fast does the machine stop when you switch it off? It would be horrible to hit the stop switch and the faceplate unscrew itself from the arbor. Maybe you could rig up something like a woodturning hand rest just clear of the face of the disk to dissuade it from this.

[Dave HalfordParticipant @davehalford22513]

Slowest speed is 85rpm – note the smoke coming off the carbide cutter from the cast iron in the video at the start disappears nearer the centre. + he is turning smaller that 14″.

That said you need to turn alloy so should be about the same.

A lenco turntable for example would have a spindle right through the platter. You could turn up an adapter shaft to fit the spindle hole from  2″ round steel stock leave a 1/4″ thick flange and make a 5/8″ or 16mm spigot to fit into your milling cutter holder. Glue it to the table and feed light and slow. Remove with blowlamp when done.

 

[DC31k]

On DC31k Said:

On Henry Bainbridge Said:

an existing threaded 30 INT shank.

Thanks for that. The obvious off-the-shelf candidate for that would be a 30 taper threaded shank for a boring head (I think they are 1 1/2″ – 18).

Yes I think that’s probably what it was. Its 1 1/4″ – 12 and came with a bunch of other tooling / arbors / adaptors etc. I would be more comfortable with 1 1/2″ – 18 so I will look out for one of those for future iterations of the same concept.

How much inertia will the setup have? Alternatively, how fast does the machine stop when you switch it off? It would be horrible to hit the stop switch and the faceplate unscrew itself from the arbor. Maybe you could rig up something like a woodturning hand rest just clear of the face of the disk to dissuade it from this.

Good point, I was more worried about the draw bar coming loose, but this is probably a much more likely scenario. The faceplate weighs just over 7lb and the part itself is about the same, so 14lb ish in total. The Centec doesn’t come to a hard stop at the slow to medium speeds, but having said that, there is a reverse switch (because the vertical spindle is driven by a mitre gear from the horizontal spindle)… so there is a risk of powering up in reverse. The table itself is quite close to the part, but only along the bottom half, and I wouldn’t want to risk damaging it. Some sort of stop across the face would definitely be a good idea.

Another thought just ocurred to me… the drive dogs on the spindle only go about half the way into the slots on the shank. If I attached another pair of dogs onto the back side of the faceplate (once it is screwed into place) that locked into the remaining half of the slots, would that suffice as a decent safety precaution? If so, what would be a good material to make the dogs from?

[DC31kParticipant @dc31k]

The boring head adaptor in 30 taper is listed by RDG.

Maybe approach the faceplate undoing with a suck-it-and-see attitude. Disconnect the reverse switch so that problem goes away.

Mount just the faceplate, spin it up way faster than you will do when turning the part and try to stop it quick and make it unscrew itself. Bolt some lumps of metal to its perimeter to amplify the problem.

If your extreme torture tests do not produce a bad result, then nor will more sedate use of it. Loctite the faceplate to the arbor.

[DC31k]

On DC31k Said:

My gut feeling is that the vertical spindle of a Centec head is not 3 1/2″ from the face of the column.

Not far off.. it’s just over 4″ between column and vertical spindle centre, so this idea could definitely work. I have a 5″ RT that fits nicely on the (admittedly quite small) Centec table. Need I worry slightly about deflection, as there would be a 4 1/2″ overhang? The part itself is just under 1/2″ thick so maybe if I am taking light passes, the overhang is not such an issue? For comparison, the faceplate is 9″ giving a 2 1/2″ overhang.

[BazyleParticipant @bazyle]

If the Centec has backgear don’t be playing games with sudden stops or you might lose some of the bull wheel teeth. Unlike a lathe the gears will not be built for high strength. Better to mount a bicycle wheel on the back of the shaft and drive it slow off another motor.
You shouldn’t be using a reversing switch for on/off. When the contacts burn out it will be much more expensive to replace or repair. Get an NVR switch.

[Henry BainbridgeParticipant @henrybainbridge40560]

Just to clarify, the reverse switch is essential because the vertical spindle is connected to the horizontal spindle via a mitre gear… so it goes the wrong way unless you reverse it.

I never suggested using the reverse switch to force a sudden stop, I am saying the suggestion of another level of safety is welcome, since there is a small chance that the machine may be powered up in reverse by mistake.

[old martParticipant @oldmart]

For maximum stiffness, I would look at a MT 3 socket outside diameter for the boss of the faceplate. The OD of the socket projects a good ammount and is cylindrical, and it might be possible for a custom drawbar shank to project right through the centre for holding the plate securely.

The suggested boring head adaptor would be a possibility for attaching the plate if you can put a compatible thread in the plate.

[TendorParticipant @tendor]

My effort to use a ‘faceplate’ on a NT30 spindle may trigger some thoughts.

The nose dimensions and tolerances of the four threaded holes, and the spindle diameter, are well defined.  I have used the four cap screws as retainers and the OD of the spindle nose as the radial locator. It has been used to date to mount a four-jaw chuck.

[Tendor]

On Tendor Said:

The nose dimensions and tolerances of the four threaded holes, and the spindle diameter, are well defined.

That is a good idea. It would be like a real old fashioned nose-mounted face mill.

Dimensions on pages 15 & 15 here:

https://theswissbay.ch/pdf/Books/Survival/Workshop/Machining%20and%20Machinery/Machinery%27s%20Handbook%20%2826th%20Edition%29/26663_yg8.pdf

Same document is here:

There is some chance that for a UK-made Centec the threads might be BSW instead of UNC.

[Tendor]

On Tendor Said:

My effort to use a ‘faceplate’ on a NT30 spindle may trigger some thoughts.

Trigger some thoughts it certainly has… thoughts I should have had, considering those 4 x threaded holes were staring me in the face the whole time 🤣

[DC31k]

On DC31k Said:

On Tendor Said:

The nose dimensions and tolerances of the four threaded holes, and the spindle diameter, are well defined.

That is a good idea. It would be like a real old fashioned nose-mounted face mill.

Not sure what that means, would be interested to see. Agreed tho, great idea and much more secure.

There is some chance that for a UK-made Centec the threads might be BSW instead of UNC.

Good point, will check 👍🏼

[DC31kParticipant @dc31k]

“Not sure what that means, would be interested to see.”

Page 80 and page 92 here:

https://archive.org/details/treatiseonmillin00cincrich/mode/2up

The whole book is superb. Their ‘Treatise on planers’ is also highly recommended.

There is another ‘Treatise on milling’ by Brown & Sharpe which might also show some.

[Henry BainbridgeParticipant @henrybainbridge40560]

That’s a great book, beautifully put together, thanks for the link.

Those bolt holes seem to have fallen out of use so it seems strange they are still included in new milling machines today, or am I missing something? I haven’t seen any tooling that obviously use them, and wouldn’t know what to search for if I wanted to. Anyway, they will definitely come in handy for this application!

[Andrew JohnstonParticipant @andrewjohnston13878]

I considered using this technique some years ago when I was asked about a job that needed a 36″ diameter disc to be turned. Ultimately the job disappeared so I never used the technique. But it’s a useful idea to have in the armoury.

In answer to Henry I have used the four holes (threaded 1/2″ BSW) on my INT40 vertical head for the horizontal mill to mount a large (160mm diameter) insert cutter.

Andrew

[Henry BainbridgeParticipant @henrybainbridge40560]

I am wondering, did the cutter have the int40 taper, or did it just use the bolts and locate against the face?

[Henry Bainbridge]

On Henry Bainbridge Said:

I am wondering, did the cutter have the int40 taper, or did it just use the bolts and locate against the face?

Please have a look in this publication. It is a gold mine.

http://vintagemachinery.org/pubs/detail.aspx?id=23911

In brief, they used a ‘centering plug’ (I think the UK models would have used a centreing plug but that is not listed in the catalogue) to locate/align the cutter but the drive and security was provided by the spindle nose.

[Henry BainbridgeParticipant @henrybainbridge40560]

Brilliant, just the info I need. So it looks like all bolt-mounted cutters use a centering plug, and larger cutters achieve added rigidity from the outer diameter of the spindle. A large faceplate definitely falls into this category, so I should be using both.

The pdf doesn’t give the spec for a 30 int centering plug, but they are available with a 1″ arbor (by Jones & Shipman) so I am going with that. I think the idea is that the drawbar keeps the plug in place, and the cutter just slides onto it (and the outside of the spingle nose) and is drawn in by just the 4 bolts. This makes sense, as I was wondering how it could locate on the taper and the face at the same time… the answer is it doesn’t.

Come to think of it, it might be hard to make an adaptor that centers on the plug and the outside of the spindle. I am relying on them being perfectly concentric… I guess I will cross that bridge when I come to it!

 

[Henry Bainbridge]

On Henry Bainbridge Said:

I am wondering, did the cutter have the int40 taper, or did it just use the bolts and locate against the face?

The cutter did not have an INT40 arbor, I just used the bolts and drive dogs. In theory some sort of centre to ensure concentricity of the cutter could be useful. But I don’t have one and, since the cutter was borrowed, it wasn’t sensible to make one. For my application, which was to see how hard I could drive the mill before it stalled, a little runout didn’t matter.

Andrew

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