Rigidity problems with a homemade Myford Saw Table

[GreensandsParticipant @greensands]

Hi – I have made up a saw table for use on my Myford S7 lathe but in its current configuration it is failing to provide the rigidity required for the sawing thin strips of BMS sheet stock. The photos hopefully show the current set up which can be summarised as follows:

1) Saw Table: Aluminium plate measuring 8.5”x6”x 3/8” thk.

2) Single support pillar: 3/4” dia BMS rod clamped to the front cross slide slot using a 3/8” dia socket headed screw backed up by a 1/8″ plate washer to help distribute the load.

3) The table is clamped to the pillar by two ¼” BSF screws located on flats milled on to the pillar.

4) Saw Blade: 4” dia x 1/32 x 1” bore fine tooth saw

5) Cutting speed: Lowest back speed

 

6) Test piece: 1/32” thk BMS clamped to the table by 4off 6mm thumb screws

My initial thoughts suggests that the problem must lay with the use of a single support column space too from back from the cutting action but then from inspection of some photos of the pucker Myford unit would indicate that although the clamping arrangement is a much more massive affair, the table is still being supported by a single column.

I would welcome any suggestions and guidance from others who have made up their own saw table for use on the Myford together with any recommendations for a suitable type of slitting saw.

 

 

 

[GreensandsParticipant @greensands]

PS: The final photo in the above sequence was added in error. Please ignore

[Michael GilliganParticipant @michaelgilligan61133]

I have not made such a thing, but please let me comment anyway:

Your support pillar looks much too lightweight and has several points of likely flexure, or even potential looseness.

A single small diameter flange on one Myford tee-slot seems to be asking for trouble.

Think bigger and beefier … think Gibraltar !

MichaelG.

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P.S. __ apart from that aspect, it looks very nicely done

[DC31kParticipant @dc31k]

There is some discussion of the Myford one here:

Help with Myford Saw Table?

Comparing the two, yours looks like it is ambitious on the length of cut it can accommmodate.

You can see the length of the gash in the Myford table. Presumably that is made so that the pillar would hit the arbor once that length is reached. Having a shorter length of cut means less cantilever and more ridgidity. The Myford table is ribbed, increasing its depth and stiffening it.

Maybe consider some stiffeners bolted to your table, with 1/16″ clearance to the top of the arbor.

With a good, repeatable fence on the attachment, you could halve the overhang (length of cut), cut halfway through, reverse the piece and cut the other half.

The Myford one does have a single column but it is (a) steel; (b) greater diameter than yours; (c) shorter than yours.

The quickest and easiest win would be to replace the column with something bigger and move it closer to the arbor.

You could try boring a rectangular piece of something the diameter of the arbor and then machining its base to sit (and slide) on the cross slide and its top top to sit (and slide) on the underside of the saw table. The best I can describe its operation is like a cross head bearing.

[Howard LewisParticipant @howardlewis46836]

Can only agree with the comments re the small single pillar support.  Bound to wave in the breeze!

As an absolute minimum install a second one in the slot at bthe other end.

Preferably, replace the single pillar by a solid support, secured at both ends, to maximise rigidity, or location and support for the table.

The “Gibraltar” toolpost is a good example of how it should be done.

Definitely brick mausoleum territory!

Howard

[noel shelleyParticipant @noelshelley55608]

I go along with the others, the single pillar to small and the table far to big ! The whole affair needs to be FAR more rigid, the Myford is cast iron, added weight, less vibration and the work clamped down ! Noel

[GreensandsParticipant @greensands]

The need to redesign the pillar now taken on board. Can anyone point me in the right direction for a detailed drawing showing the Gibraltar toolpost?

[Michael GilliganParticipant @michaelgilligan61133]

It was just a general ‘philosophy’ … but here you go:

https://www.hemingwaykits.com/HK1090

MichaelG.

[Anonymous]

I’d bin the saw table and mount the work, on a sacrifical plate, directly onto the cross slide. It looks like the 4″ diameter saw clears the table. If not use a 3″ diameter saw. A smaller diameter saw will be less likely to walkies. Depending upon the thickness of the work a coarse tooth saw should be used for better swarf clearance. It might be a trick of the photography but the saw looks to be blunt. I would also mount one end other saw arbor in a chuck, or collet, and move the saw as close as possible to the chuck. That should stiffen up the arbor and hence the saw.

Andrew

[JasonBModerator @jasonb]

Make a “C” shaped support for the rear of the table that passes around the back of the arbour so you can get the full length cut, lower the table so it just clears the arbour and Like Andrew says check the blade is sharp as it looks well worn in the photo.

Bolting the table straight onto the cross slide would also be an option and feed from back towards you to avoid climb cutting.

[Andrew Johnston]

On Andrew Johnston Said:

I’d bin the saw table and mount the work, on a sacrifical plate, directly onto the cross slide.

There may be some difficulties with that approach.

If you keep the rotation direction the same, and feed from front to back it is climb cutting and will suck the workpiece into the teeth or with a skinny arbor could climb up on top and bend it like a banana.

The challenges of running in reverse on a Myford with a threaded spindle nose has been discussed before. If you chose to run in reverse, it may need an opposite hand nut on the arbor.

Even if you start at the back and saw towards you, rotating conventionally, the saw is then trying to lift the workpiece off its support.

[Nigel Graham 2Participant @nigelgraham2]

You could increase the rigidity of the table itself by screwing two pieces of angle to its underside, to reduce the plate flexing, and extended back to pick up pillars in the rear T-slot.

Also modify the pillars, or replace them with blocks, so the table goes below the arbor; and turn the blade round so the feed is against its rotation.

[Michael GilliganParticipant @michaelgilligan61133]

I doubt if the stiffness of the plate is a problem

Most engineering metals have a similar ‘specific stiffness’ [stiffness to weight ratio] which gives them broadly similar vibration characteristics. … I feel quite sure that Greensands’ problem relates to the support pillar itself, and its attachment to the Myford slide.

MichaelG.

[DC31k]

On DC31k

There may be some difficulties with that approach.

The current approach isn’t working, so it has some difficulties too.

Personally i don’t worry too much about climb milling, just tighten the gib strip a little. As previously noted running a long arbor between centres isn’t the best setup for rigidity.

From the OPs picture it seems that the work is clamped along its full length so there shouldn’t be a problem with work lifting. All my slitting of material has been done on the horizontal mill with large DOC (up to 12mm) and I’ve never had a problem with  the work lifting. Just use a few clamps.

Andrew

[Dave HalfordParticipant @davehalford22513]

Is a loose drive dog OK with an intermittent cut?

The piece being cut is only clamped at 4 points with thumb screws wouldn’t it be better to fully clamp with the whole bar and then tighten the screws?

Just asking I have no experience except on a mill and anything that can chatter will given half a chance.

[Howard LewisParticipant @howardlewis46836]

If you can live with climb milling, by tightening the gibs, to prevent the work feeding itself into the cutter, you can stiffen the work table, (But the important thing is to make the supports as rigid as possible)

Doubling the thickness of the table will increase its stiffness by a factor of eight.

With regard to clamps, rather than finger tightened clamps, I would use a spanner on hexagon fasteners (nuts and studs or setscrews) to clamp the work.

Howard

[GreensandsParticipant @greensands]

Assuming that rigidity problems can be sorted out I would like some guidance on the selection of lathe speeds on the Myford as I can’t recall seeing any reference to the recommended speeds when using a slitting saw between centres. I have been using the lowest back speed but presumably it is possible given a sharp saw blade and a rigid set-up to run at higher speed settings.  All other things being equal is it correct to say  that a 3” diameter slitting saw would impose less of a stress on the set up than a 4” saw?

[FulmenParticipant @fulmen]

A rear support on the other side of the shaft should sort out most of your problems. As for speeds you really have to see what works. Max speeds are the same as for other machining, but chances are you need to run it fairly slow to avoid chatter. That’s OK, at least with HSS.

 

[jaCK HobsonParticipant @jackhobson50760]

In theory I think deflection of a cantilever beam for a given force is proportional to the length cubed. The vertical post can be approximated as a cantilever, as well as the table. As has been suggested, easiest way to stiffen them is to minimise the lengths…. or don’t use a cantilever and support at other end. Support at other end would change the table to a simple supported beam at both ends, and almost remove the vertical post from the equation.

Support at both ends moves the point of max defelction to middle of beam, at 1/4 the deflection of the cantilever.

In practice, make it massive everywhere, supported everywhere. I’m amazed how floppy my S7 and my desktop mill are.

[jaCK HobsonParticipant @jackhobson50760]

Another idea… it is the change in deflection due to change in cutting forces that is the biggest issue. If you pre-load the beam from the top via something very stiff then this reduces deflection also. Much more theoretical than practical value probably.

[Greensands]

On Greensands Said:

Assuming that rigidity problems can be sorted out I would like some guidance on the selection of lathe speeds on the Myford..

 

..other things being equal is it correct to say  that a 3” diameter slitting saw would impose less of a stress on the set up than a 4” saw?

(for BMS) ..somewhere between 100 & 200rpm for a 3″, and 70 & 150 rpm for a 4″ – start at the slower end and see how it feels; everything from saw ‘newness’ to the quality of the material you are cutting seems to have a bearing when it comes to slitting and I find it a business where sensitivity on the part of the operator definitely plays some part in a happy outcome. Do try and keep it cutting positively, and don’t whatever you do, put CT90 anywhere near it – it’s much too sticky for this job.

The query about cutter diameter is interesting.

My own take and feeling is that cutter Dia. doesn’t make much difference at the workface, because here it is chip load that makes itself felt and all other things being equal you probably want this to be about the same regardless of cutter diameter.

The loading at the cutter mounting / arbor & spindle do feel the difference in cutter diameter, but in my experience the commonest issues are saw slippage or ‘stalling’ – the first mitigated by attentiveness when mounting and the second probably not very likely on a ‘7’ in backgear, unless you are seriously overdoing it.

In general (with thin blades), I find it best to select the smallest blade that will clear the work – just because they are stiffer – but with a ‘table’ set up such as yours I might be less certain.

I’d be interested to know whether other users think there’s any advantage to using the ‘front quarter’ of the blade to get fewer teeth taking a more direct path through the material, vs. the rather ‘tangential’ cut that you have running the material at the very top of the blade..?

When cutting thinner material I generally try to run the saw in about ‘three-quarters of the way out’

 

 

 

[bernard towersParticipant @bernardtowers37738]

Original must have had the same problems as yours doesn’t look too different to one being advertised on the bay and there are no comments from actual users!!!!

[Michael GilliganParticipant @michaelgilligan61133]

I have to say, Bernard … it looks substantially different to me: in several areas, most notably the broad-based attachment to the cross-slide.

MichaelG.

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Compare fixing arrangement with second photo in the opening post.

[Michael GilliganParticipant @michaelgilligan61133]

Useful discussion … and several good photos on this thread from 2017:

https://www.model-engineer.co.uk/forums/topic/help-with-myford-saw-table/

MichaelG.

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P.S. __ No, I don’t have one, but I have admired them from an impoverished distance for a long while now.

[Michael Gilligan]

On Michael Gilligan Said:

I have to say, Bernard … it looks substantially different to me: in several areas, most notably the broad-based attachment to the cross-slide.

MichaelG.

..also worth noting how little of the ‘shank’ must remain unsupported once it’s home in the lower bracket..

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