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                                                                     Exhibit 8.1

                                                , 1999

ACT Manufacturing, Inc.
2 Cabot Road
Hudson, Massachusetts 01749

Ladies and Gentlemen:

   We have acted as counsel for ACT Manufacturing, Inc., a Massachusetts
corporation ("Parent"), in connection with the preparation and execution of the
Agreement and Plan of Merger and Reorganization (the "Agreement") dated as of
May 10, 1999, among Parent, East Acquisition Corp., Inc., a Delaware
corporation and a wholly-owned subsidiary of Parent ("Sub"), and CMC
Industries, Inc. a Delaware corporation ("Company"). This opinion is being
delivered to you pursuant to Section 6.01(d) of the Agreement. Pursuant to the
Agreement, Sub will merge with and into Company (the "Merger"), the separate
corporate existence of Sub will cease and Company will continue as the
surviving corporation and as a wholly-owned subsidiary of Parent. Unless
otherwise defined, capitalized terms referred to herein have the meanings set
forth in the Agreement. All section references, unless otherwise indicated, are
to the Internal Revenue Code of 1986, as amended (the "Code").

   You have requested our opinion regarding certain United States federal
income tax consequences of the Merger. In delivering this opinion, we have
reviewed and relied upon the facts, statements, descriptions and
representations set forth in the Agreement (including the Exhibits, the
Schedules and the Parent and Company Disclosure Schedules), and such other
documents pertaining to the Merger as we have deemed necessary or appropriate.
We have also relied upon certificates of officers of Parent and Sub, and of
Company, respectively (the "Officers' Tax Certificates").

   In connection with rendering this opinion, we have assumed (without any
independent investigation) that:

   1. Original documents (including signatures) are authentic, documents
submitted to us as copies conform to the original documents, and there has been
due execution and delivery of all documents where due execution and delivery
are prerequisites to effectiveness thereof;

   2. Any statement made in any of the documents referred to herein "to the
best of the knowledge" of any person or party or similarly qualified is correct
without such qualification; and

   3. All statements, descriptions and representations contained in any of the
documents referred to herein or otherwise made to us are true and correct in
all material respects and no actions have been (or will be) taken which are
inconsistent with such representations.

   Based on our examination of the foregoing items and subject to the
assumptions, exceptions, limitations and qualifications set forth herein, we
are of the opinion that, if the Merger is consummated in accordance with the
provisions of the Agreement and the statements set forth in the Officers' Tax
Certificates are true and correct, then, for United States federal income tax
purposes, the Merger qualifies as a "reorganization" as defined in Section
368(a) of the Code.

   This opinion represents and is based upon our best judgment regarding the
application of United States federal income tax laws arising under the Code,
existing judicial decisions, administrative regulations and published rulings
and procedures. Our opinion is not binding upon the Internal Revenue Service or
the courts, and there is no assurance that the Internal Revenue Service will
not successfully assert a contrary position. Furthermore, no assurance can be
given that future legislative, judicial or administrative changes, on
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ACT Manufacturing, Inc.
      , 1999
Page 2

either a prospective or retroactive basis, will not adversely affect the
accuracy of the conclusions stated herein. Nevertheless, we undertake no
responsibility to advise you of any new developments in the application or
interpretation of the United States federal income tax laws.

   This opinion addresses only the classification of the Merger as a
reorganization under Section 368(a) of the Code, and does not address any other
federal, state, local or foreign tax consequences that may result from the
Merger or any other transaction (including any transaction undertaken in
connection with the Merger).

   No opinion is expressed as to any transaction other than the Merger as
described in the Agreement or to any transaction whatsoever, including the
Merger, if all the transactions described in the Agreement are not consummated
in accordance with the terms of such Agreement and without waiver or breach of
any material provision thereof or if all of the representations, warranties,
statements and assumptions upon which we relied are not true and accurate
through the Effective Time and at all relevant times thereafter. In the event
any one of the statements, representations, warranties or assumptions upon
which we have relied to issue this opinion is incorrect, our opinion might be
adversely affected and may not be relied upon.

   This opinion is intended for the benefit of Parent and may not be relied
upon or utilized for any other purpose or by any other person and may not be
made available to any other person without our prior written consent.

                                             Very truly yours,

                                             TESTA, HURWITZ & THIBEAULT, LLP