Re: Motor starting jolt

Guenther Paul

If a jolt means a electrical shock at startup , i would check the grounding of the electrical supply and system   RPM have no play in it

From: "Ray De Jong dejongray@... [SOUTHBENDLATHE]"
To: "John M Griffin griffinjohnm@... [SOUTHBENDLATHE]" <SOUTHBENDLATHE@...>
Sent: Monday, December 25, 2017 1:40 PM
Subject: Re: [SOUTHBENDLATHE] Motor starting jolt

The motor has 2 (two) things wrong in my estimation #1 - it is a quick start motor as in last reply.
Worst of all though #2 - it is too high speed for your lathe, it should be a 1725 (nominal).
South Bend lathes were only supplied with the lower speed motors and would only be useable at 3450rpm if a further speed reduction was used; as with the "as supplied pulley arrangement" a 3600 rpm motor will run the spindle at too high speed for the headstock bearings (sleeves) and would be too high speed for machining most metals unless run in back gear.
I could be wrong about this but I have operated and have owned a number of SB's from 9" to 16" and have not yet encountered a higher than 1725rpm motor except on one 14" inch line-driven SB that we converted to 4spd. automotive transmission and we used an 1140rpm motor on a 2:1 reduction from the motor to jackshaft then from the transmission output shaft onto the middle pair of flat belt pulleys
hopefully this will help

On Monday, December 25, 2017, 9:58:03 AM PST, John M Griffin griffinjohnm@... [SOUTHBENDLATHE] wrote:

Induction motors designed to deliver big starting torque (eg, compressor duty) can give a jolt when hooked up to something like a table saw or a lathe

eg, "The 1 HP LEESON Compressor Duty Electric Motor is a dependable and powerful single-phase motor designed especially for compressors requiring high breakdown torque and rugged mechanical construction. UL listed. CSA certified." 

LEESON Compressor Duty Electric Motor — 1 HP, 115/230V, 3600 RPM, Model# 110160

The issue is high inrush current. If you wired in a particularly stiff (high current) 115 VAC circuit in your shop, this will amplify the issue. One remedy is to wire from the outlet to the motor using a wire size and length calculated by the motor full load running current (on motor tag). This will dampen start up jolt.

The above motor is FL rated at about 13A. Just for grins, splice in a 25' - 50' roll of 14 AWG between 115 VAC outlet and motor then test. This approach would be a lot cheaper than a solid state soft start

On Sun, Dec 24, 2017 at 7:01 PM, Oren obolt@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:
I’m thinking a soft starter would manage incoming line voltage but would not reduce the initial surge coming from the starting capacitor. I believe it’s that starting capacitor that generates the big jolt making the motor jump at startup. I could be totally wrong for sure as I’m over my head on this.

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