<SEC-DOCUMENT>0001127602-11-023123.txt : 20110809
<SEC-HEADER>0001127602-11-023123.hdr.sgml : 20110809
<ACCEPTANCE-DATETIME>20110809163417
ACCESSION NUMBER:		0001127602-11-023123
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20110805
FILED AS OF DATE:		20110809
DATE AS OF CHANGE:		20110809

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Knutson Jeffrey Scott
		CENTRAL INDEX KEY:			0001341537

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-07635
		FILM NUMBER:		111021301

	MAIL ADDRESS:	
		STREET 1:		1328 RACINE STREET
		CITY:			RACINE
		STATE:			WI
		ZIP:			53403

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TWIN DISC INC
		CENTRAL INDEX KEY:			0000100378
		STANDARD INDUSTRIAL CLASSIFICATION:	GENERAL INDUSTRIAL MACHINERY & EQUIPMENT [3560]
		IRS NUMBER:				390667110
		STATE OF INCORPORATION:			WI
		FISCAL YEAR END:			0119

	BUSINESS ADDRESS:	
		STREET 1:		1328 RACINE ST
		CITY:			RACINE
		STATE:			WI
		ZIP:			53403
		BUSINESS PHONE:		2626384000

	MAIL ADDRESS:	
		STREET 1:		1328 RACINE STREET
		CITY:			RACINE
		STATE:			WI
		ZIP:			53403

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	TWIN DISC CLUTCH CO
		DATE OF NAME CHANGE:	19770217
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-08-05</periodOfReport>

    <issuer>
        <issuerCik>0000100378</issuerCik>
        <issuerName>TWIN DISC INC</issuerName>
        <issuerTradingSymbol>TWIN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001341537</rptOwnerCik>
            <rptOwnerName>Knutson Jeffrey Scott</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>TWIN DISC, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>1328 RACINE ST.</rptOwnerStreet2>
            <rptOwnerCity>RACINE</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53403</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>Corporate Controller</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-08-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>522</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>36.13</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17643</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2011-08-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1169</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>38.1105</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16474</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $37.48 to $38.35, inclusive. The reporting person undertakes to provide to Twin Disc, Incorporated, any security holder of Twin Disc, Incorporated, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote to this Form 4.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Jeffrey S. Knutson</signatureName>
        <signatureDate>2011-08-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
