Earlier today, Joy Global (NASDAQ:JOYG), one of the world's top producers of mining machinery and equipment, reported a pretty solid set of results that gave long-suffering investors a chance to rejoice and sent the stock price up over $6.00 per share, which is a gain of over 18%.

The company, which has seen its share price dive more than 40% since its late-April highs due to concerns about capacity constraints and weakness in the domestic coal industry, announced that revenue for the three months ended July 29 climbed to $599 million, up 17% but just south of Street expectations of $613 million. The main driver of growth was its aftermarket parts and services business, which saw revenue climb 24% to $377 million while original equipment sales increased at a more measured rate of 5.8%.

The increase in the higher margin aftermarket business -- to around 63% of Joy Global's total revenue, from 59% last year -- drove an improvement in gross margins to 32% from 28%. Operating margins came in at 18.3%, up nicely from the 14% reported in last year's quarter.

As a result of this pleasant combination of revenue growth and margin expansion, net income (excluding a one-time tax gain of $0.90) came in at $0.63 per share, 9% ahead of Street expectations and 66% ahead of last year's earnings (again, excluding one-time items) of $0.38 per share.

In addition to these improved operating metrics, the company announced that bookings during the quarter rose 13% to $606 million and that it had repurchased some 3.8 million shares at a total cost of roughly $197 million.

I'm also heartened by the fact that Joy's planned 40% capacity expansion of its mining shovel plant in Milwaukee is on schedule for completion by the end of 2006, especially since the company's P&H Mining division simply couldn't fill all the orders it received during the quarter. That capacity increase, as well as the acquisition of additional capacity through bolt-on acquisitions, like the company's recent purchase of Stamler (for $117 million, or less than one times sales), should go far in alleviating Wall Street concerns about a continued bottleneck in production.

All in all, with shares of Joy Global trading at a reasonable 14 times fiscal 2007 estimates (despite today's mammoth gain) -- a 30% discount to the company's projected long-term growth rate -- it might be time for investors to consider adding a little Joy to their portfolios.

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Fool contributor Will Frankenhoff does not own shares in any of the companies mentioned above. The Fool has a disclosure policy.