* Copper prices set to log 4 pct weekly gain * Tin hovers around 6-month high * Coming up: euro zone consumer confidence at 1400 GMT By Silvia Antonioli and Melanie Burton LONDON/MELBOURNE, Sept 20 (Reuters) - Copper firmed on Friday and was on track for its biggest weekly gain in a year, after the U.S stuck to its commodity-friendly stimulus programme, although a stronger dollar limited gains. The U.S. Federal Reserve shocked markets on Wednesday, saying it would maintain bond purchases at their present pace, confounding expectations of a scaling-back in asset purchases from the current $85 billion a month. Fuelled by the Fed decision, copper prices have rallied more than 4 percent this week, building on a recovery from late June's 3-year lows on signs of economic stabilisation in top consumer China. Benchmark copper on the London Metal Exchange inched up 0.1 to $7,343.75 a tonne by 0946 GMT, after 2.1 percent gains in the previous session. Prices hit $7,357 a tonne on Thursday, the highest since Aug. 27. "The risk-on rally that followed the Fed's decision late on Wed to abstain from tapering for now is benefited base metals however these gains were mostly macro driven and sustained gains from here will depend on fundamentals," VTB Capital analyst Andrey Kryuchenkov said. "The market is broadly balanced this year, heading into a larger surplus next year but seasonal demand from Chinese fabricators should still help prices with a pick up in activity before the year end." Weighing on metals the dollar edged off a seven-month low against a basket of currencies. A stronger U.S. unit makes dollar-priced commodities costlier for holders of other currencies. TIN GAINS Benchmark tin was little changed at $23,285 from $23,290 at the close on Thursday when the metal hit a 6-month top at $23,350. Prices of the metal were boosted by strict rule changes on shipments from top exporter Indonesia, which has some electronics makers seeking to diversify supply. The Rwandan subsidiary of British mining firm Pella Resources Ltd plans to invest $22 million in the east African country's small mining industry to extract tin ore, according to a deal signed by both sides on Thursday. Zinc, used to galvanize steel was at $1,902 from $1,906 Thursday's close while stainless steel ingredient nickel was at $14,390 from $14,400. Battery material lead was at $2,104.75 from $2,126 and aluminium was at $1,822.50 from $1,829.

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