Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 973,277	$ 1,442,116
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	613,167	607,477
(Gain) loss from disposal of equipment	(1,600)	318
Deferred income taxes	(48,000)	(15,000)
Changes in operating assets and liabilities:
Accounts receivable	(629,324)	(840,290)
Inventories	(458,150)	(452,996)
Other current assets and prepaid income taxes	7,372	337,461
Accounts payable	288,102	469,508
Accrued wages and salaries	161,600	281,228
Other accrued expenses	(58,057)	4,555
Unearned revenue and customer deposits	(34,395)	(203,457)
Net cash provided by operating activities	813,992	1,630,920
Cash flows from investing activities:
Capital expenditures	(796,258)	(936,111)
Proceeds from the sale of equipment	1,600	1,022
Proceeds from certificates of deposit	3,328,000	2,988,000
Purchases of certificates of deposit	(2,083,000)	(2,988,000)
Net cash provided by (used in) investing activities	450,342	(935,089)
Cash flows from financing activities:
Cash dividends paid	(724,599)	(589,341)
Net cash used in financing activities	(724,599)	(589,341)
Net increase (decrease) in cash and cash equivalents	539,735	106,490
Cash and cash equivalents at beginning of period	353,475	800,894
Cash and cash equivalents at end of period	893,210	907,384
Supplemental schedule of non-cash investing activities:
Capital expenditures in accounts payable	$ 2,900	$ 2,585