REVENUE - Disaggregation of Revenue (Details) - USD ($)	3 Months Ended
	Jul. 31, 2020	Jul. 31, 2019
Disaggregation of Revenue
Amount of impairment losses	$ 0	$ 0
Net sales	6,019,000	6,346,000
Domestic
Disaggregation of Revenue
Net sales	5,898,000	6,098,000
Foreign
Disaggregation of Revenue
Net sales	121,000	248,000
Commercial Aerospace
Disaggregation of Revenue
Net sales	925,000	2,410,000
Defense
Disaggregation of Revenue
Net sales	4,869,000	3,823,000
Industrial
Disaggregation of Revenue
Net sales	225,000	113,000
Magnetic components
Disaggregation of Revenue
Net sales	3,963,000	3,254,000
Potted coil assembly
Disaggregation of Revenue
Net sales	1,735,000	1,519,000
Electro-mechanical assemblies
Disaggregation of Revenue
Net sales	$ 321,000	$ 1,573,000