Building a small bench

[Howard LewisParticipant @howardlewis46836]

Is it a resonance, which only happens at one speed?

If the frequency changes with lathe speed, it is just old fashioned vibration.

Either way, isolating the lathe from the bench, with suitable mounts should cure the problem.

Either that or bolt on a great lump of concrete to the bottom of the bench, so that the lathe lacks the energy to excite it!

Howard

[JAParticipant @ja]

I have run the lathe over a number of speeds this afternoon and the bench resonance is not pronounced and only occurs at the lowest speed without back gearing. If it is there it is well damped and I have decided it is not a concern. I do suspect the bench top is vibrating but its Q factor would be very low. A cross member or another sheet of ply would shift the frequency higher.

The bench is very firmly on the ground.

JA

[Howard LewisParticipant @howardlewis46836]

Ear Defenders will probably prevent you hearing how the cut is going.

Now, to find something with the same natural frequency, which will vibrate 180 degrees out of phase!

Either that or some means of increasing the inertia of the bench top so that the natural frequency then lies between minimum "normal speed" and maximum in Back Gear, so that area is never visited.

Howard

[BazyleParticipant @bazyle]

I like the way you have incorprated the Bisley and teh space for the stool.
As the top is virtually impossible to remove perhaps you can lift up a piece of paving slab into the space under the lathe and hold it with battens at the sides that don't get in the way of your knees. Another good option would be to put a sheet of ply across the underside of this space and fill the cavity with dry sand. In fact you could experiment with small bags of dry sand positioned around the lathe.

[Frances IoMParticipant @francesiom58905]

I have a Perris ME90 a precursor to the Cowell – you certainly don’t need ear defenders for use! My Perris is mounted on a board – the motor is an old one so quite heavy but the board has rubber feet and doesn’t seem to make my bench vibrate, admittedly it is somewhat heavier with timber twice the thickness and height adjusters with rubber feet

[Howard LewisParticipant @howardlewis46836]

The ear defenders would be needed for a Bench top in resonance, NOT the machine. Obviously there is a speed where the lathe sets the bench top into resonance, causing a barely acceptable noise level

To avoid this, given that the frequency is low, it cannot be absorbed.. The solution has to be either to decrease the amplitude by damping, or to tune it out.

The paving slab / sand bag suggestions will lower the frequency, not into the Back Gear operating range, we hope.

Howard

[Martin KyteParticipant @martinkyte99762]

Is the bench top resonating or the backboard? Are you getting issues with surface finish?

regards Martin

[JAParticipant @ja]

I happily used the lathe this afternoon, turning mild steel at 280 and 880 rpm without any problems. The finish was good. It could have been improved to a good polish if I knew how to reduce the traverse speed (the joys of learning a new lathe). I could listen to the cut (I don't know where the idea of ear defenders came from).

I am happy and I think I have been too critical about resonace although Martin has a point about the backboard. It is the least stiff part of the bench.

At present the lathe is just sitting on the bench. When I return to it in a couple of days time I shall try rubber pads under the four corners.

JA

[JAParticipant @ja]

The problem has been cured by putting a small, single thickness, piece of inner tube rubber under each foot. It is now as sweet as a nut.

JA

[Howard LewisParticipant @howardlewis46836]

To refine the feed rate, set up changewheels to give the maximum reduction ratio between the Mandrel and the Leadscrew.

As an example, on a mini lathe this is Mandrel 20T, stud 80T and 20T, Leadscrew 80T. This gives a reduction of 16:1, so with a 1.5 mm Leadscrew the feed will be 0.09375mm /rev or 0.0037"/rev if you are an Imperialist.

With a sharp tool set on centre height, this should give quite a good finish, especially if the tool has a small nose radius.

Howard.

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