<PAGE>
 
                                                                    EXHIBIT 10.1

                      FIRST AMENDMENT TO CREDIT AGREEMENT
                             (with Borrowing Base)
                                   AND NOTE

THIS FIRST AMENDMENT TO CREDIT AGREEMENT (with Borrowing Base) and Note (this
"Amendment") dated effective as of October 1, 1997 (the "Effective Date"), is by
and between DTM CORPORATION ("Borrower") and TEXAS COMMERCE BANK NATIONAL
ASSOCIATION, a national banking association whose principal office is located in
Houston, Texas ("Bank").

PRELIMINARY STATEMENT. Bank and Borrower entered into a Credit Agreement (with
---------------------
Borrowing Base) dated as of August 6, 1997 (the "Credit Agreement"). The
"Agreement", as used in the Credit Agreement shall a1so refer to the CredIt
Agreement as amended by this Amendment. All capitalized terms defined in the
Credit Agreement and not otherwise defined herein shall have the same meanings
herein as in the Credit Agreement.

In order to induce Bank to make Loans under the Credit Agreement and to waive
compliance by Borrower with certain requirements of the Agreement through June
1, 1998. The B.F.Goodrich Company, a New York corporation, (the "Guarantor") has
agreed to provide a continuing limited guaranty of payment in the form of
Exhibit A hereto ("Guaranty") and Bank is willing to make Loans subject to the
terms and conditions set forth in the Credit Agreement as amended by this
Amendment.

NOW THEREFORE, in consideration of the premises and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged,
Bank and Borrower agree as follows.

1.   Section 1.2 of the Credit Agreement is amended by adding the following to
the end of Section 1.2 of the Credit Agreement:

     Notwithstanding the foregoing, through June 1, 1998, the "Borrowing Base"
                                                               --------------
     will be the principal dollar amount to which the Guarantor's Guaranty is
     limited."

Each of Borrower and Guarantor understands that due to the amount of Guarantor's
Guaranty the Borrowing Base cannot exceed $2,000,000.00 as of October 1, 1997
             --------------
and the maximum amount that may be borrowed subject to the terms of the
Agreement is $2,000,000.00 through June 1, 1998, effectively reducing the
Commitment to $2,000,000.00 for purposes of calculating the Commitment Fee under
Section 1.4 through June 1, 1998.

2.   Exhibit A.1 of the Credit Agreement is amended by replacing prior Exhibit
A.1 with the Exhibit B.1 attached to and incorporated into this Amendment and
the Credit Agreement for all purposes. Exhibit A.2 of the Credit Agreement is
amended by replacing prior Exhibit A.2 with the Exhibit B.2 attached to and
incorporated into this Amendment and the Credit Agreement for all purposes.

3.   Section 2.1(b) of the Credit Agreement is amended to read as follows:

     "2.1(b) Bank as received the following, duly executed and in Proper Form:
     (1) copy of Borrower's investment's policy, (2) Borrowing Base Report
     within the time required by this Agreement, (3) A Request for Loan,
     substantially in the form of Exhibit 2.1 (b), not later than one (1)
                                  ---------------
     Business Day before the date which shall also be a Business Day of the
     proposed Loan signed by a representative of Borrower and Guarantor;
     provided however, Bank may accept and act upon verbal advance requests
     received from Borrower's and Guarantor's representative reasonably believed
     by Bank to be authorized to make such requests as of the Effective Date of
     this Amendment but, until the loan is approved in writing by Guarantor, the
     Loan is not subject to the payment guaranty of the Guaranty but is subject
     to this



                               Page 1 of 3 Pages
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     Agreement and the other Loan Documents. The authorized representatives to
     request Loans are listed on the attached Schedule A. Bank may rely on
     Schedule A until Bank receives from Borrower and Guarantor a written notice
     of a change in the authorized representatives to approve a Loan. A fax from
     the Guarantor showing a signature of an authorized representative on a Loan
     Request shall satisfy the requirement that the Loan be approved in writing
     to be subject to the payment guaranty of the Guaranty. Any request for Loan
     may be executed in counterparts; and (4) such other documents as Bank
     reasonably may require."

4.   Exhibit B of the Credit Agreement is amended by replacing Exhibit B with
the Exhibit 2.1(b) attached to this Amendment.

5.   This Amendment shall become effective as of the Effective Date upon its
execution and delivery by each of the parties named in the signature lines below
and execution and delivery by Guarantor of the Guaranty and the Certificate of
Incumbency in Proper Form and payment of the Closing Fee of $5,000.00.

6.   Borrower further acknowledges that each of the other Loan Documents is in
all other respects ratified and confirmed, and all of the rights, powers and
privileges created thereby or thereunder are ratified, extended, carried forward
and remain in full force and effect except as the Credit Agreement and the Note
are amended by this Amendment.

7.   This Amendment and the Guaranty shall be included within the definition of
"Loan Documents" as used in this Agreement.

8.   WAIVER AGREEMENT: Bank has agreed to waive compliance with the following
requirements imposed upon Borrower as described and limited below for the time
period from August 6, 1997 through June 1, 1998:

 .    The requirement in 2.1(b)(2) to submit a Borrowing Base Report with a
     Request for a Loan or to submit on a monthly or weekly basis as required by
     the Borrowing Base Report and Exhibit C and Section 4.3;

 .    The requirement in 2.1(e) that the asset audit by Bank be found acceptable
     to the Bank in its sole judgment;

 .    The representation in 3.2 regarding material adverse change and change in
     the condition, financial or otherwise, of the Borrower and its Consolidated
     Subsidiaries;

 .    The representation in Section 3.4 that neither Borrower nor any Subsidiary
     of Borrower is in default in the payment of any other material agreement to
     which it is party;

 .    The requirement to comply with the lockbox requirements and to provide
     notice to account debtors of the Lockbox contained in 4.9 & 4.10 and 5.9;

 .    The restriction on additional indebtedness and liens in section 5.1 & 5.2;

 .    Compliance with the financial covenants required by 5.3 as described in
     Exhibit CB.1, 2, & 3 (Tangible Net Worth; Quick Ration and EBITDA); and

 .    The Events of Default described in 6.1(b) (c) & (d) but only as they relate
     to Borrower as Obligor and, as to (c) and (d), only as to the covenants
     that have been waived for purposes of 6.1(d).

The waivers contained herein do not constitute a waiver of any other defaults
not described in this Amendment that may currently exist or that may hereafter
occur. Bank's delay in exercising any of its rights under the Credit Agreement
does not constitute a waiver of any rights or interests of Bank except as
specifically agreed to in writing by Bank. Bank has the right to refuse to make
a Loan at any time that Borrower is not in compliance with the terms of the
Agreement as amended by this Amendment. If Bank elects to make any Loans to
Borrower while Borrower is out of compliance with


                              Page 2 of 3 Pages  
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the Agreement or during the existence of an Event of Default, the making of the
Loan shall not constitute a waiver of any defaults then existing or thereafter
arising under the Agreement, and will not constitute the agreement of Bank to
make further Loans. This Section constitutes the only evidence of Bank's waiver
of compliance with the above cited Sections of the Credit Agreement and then
only for the period described in this Amendment.

9.   Amendment to the Note - The Revolving Promissory Note dated August 6, 1997,
in the original principal amount of $6,000,000.00 (which is hereby reduced to
$2,000,000.00 by virtue of this Amendment) executed by Borrower and delivered to
Bank is amended by replacing: "(i) the sum of the Prime Rate (as hereinafter
defined) from time to time in effect plus three-quarters of one percent (3/4%),
(the "Stated Rate") or," in the first paragraph, with "(i) the sum of the Prime
Rate (as hereinafter defined) from time to time in effect minus one and one-half
                                                          -----
percent (1.5%), (the "Stated Rate") or, The "Note" as used in the Credit
Agreement and the Note shall refer to the Note as amended by this Amendment.

10.  This Amendment may be executed in any number of counterparts and by
different parties hereto in separate counterparts, each of which when so
executed shall be deemed an original and all of which taken together shall
constitute but one and the same agreement.

11.  THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF TEXAS AND AS APPLICABLE, THE LAWS OF THE UNITED STATES OF
AMERICA.

THIS WRITTEN AMENDMENT AND THE OTHER LOAN DOCUMENTS CONSTITUTE A "LOAN
AGREEMENT" AS DEFINED IN SECTION 26.02(a) OF THE TEXAS BUSINESS & COMMERCE CODE,
AND REPRESENTS THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS
OF THE PARTIES.

THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be executed
effective as of October 1, 1997.


BORROWER: DTM CORPORATION

By:     /s/ John S. Murchison, III
    ------------------------------------------
Name:      John S. Murchison, III
           President & CEO
Address:   1611 Headway Circle
           Building 2
           Austin, Texas 78754


BANK: TEXAS COMMERCE BANK NATIONAL ASSOCIATION

By:    /s/ Donna Tanner-Day
    ------------------------------------------   
Name:      Donna Tanner-Day, 
           TCB-Austin, Vice President
Address:   P.O. Box 550
           Austin, Texas 78789


                               Page 3 of 3 Pages
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                                EXHIBIT 2.1(b)
                               REQUEST FOR LOAN
                            Letterhead of Borrower
                       May be executed in Counter Parts

Texas Commerce Bank National Association
700 Lavaca
P.O. Box 550
Austin, Texas 78789-0001


Re:     Request for Loan under Agreement

Attention: Donna Tanner-Day

     This letter confirms our oral or telephonic request of ________________,
19__, for a Loan in accordance with that certain Credit Agreement dated as of
August 6, 1997, as amended effective as of October 1, 1997 (the "Agreement"),
between you and us. Any term defined in the Agreement and used in this letter
has the same meaning as in the Agreement.

     The proposed Loan is to be in the amount of $_________ and is to be made on
_____________________, 19__, which is a Business Day at least ___ Business Days
after the date of this letter. The proceeds of the proposed Loan should be
(check one:) [_] deposited into account number ________________ with the Bank
[_] _______________________________________________

     The undersigned hereby certifies that;

     (1)  The representations and warranties made by Borrower or by any other
          Person in the Agreement and the other Loan Documents are true and
          correct in all material respects on and as of this date as though made
          on this date except for those described in the First Amendment dated
          October 1, 1997.

     (2)  The proposed Loan complies with all applicable provisions of the
          Agreement.

     (3)  [_] No event of Default has occurred and is continuing that has not
          been waived by the First Amendment to the Agreement dated October 1,
          1997.

          [_] The following Event of Default exists. __________________________

          _____________________________________________________________________


                                             Sincerely,

                                             BORROWER: DTM CORPORATION

                                             By:
                                                --------------------------------
                                             Name:                              
                                                  ------------------------------
                                             Title:                             
                                                   -----------------------------

AND  The payment of the Loan requested above will be guaranteed pursuant to the
---
     Guaranty dated October 1, 1997 executed and delivered to Bank by the
     undersigned Guarantor.

                                             GUARANTOR: THE B.F.GOODRICH COMPANY

                                             By:
                                                --------------------------------
                                             Name:
                                                  ------------------------------
                                             Title:
                                                   -----------------------------