I have a 30 year old Olsen Duomatic coal wood electric combination furnace. The center grate broke about 5 years ago. Reluctant to spend 250 bucks to replace it I did a very simple rebuild which I'de like to share. First,measure the diameter of the round part of the grate where it is supported by the anchors at both ends. Then measure the full length of the broken grate. Purchase a steel dowel of the same diameter or possibly a stainless one if burning coal, and cut it to the appropriate length. The next step might be more difficult. Find a rock crushing business in your town and ask them if they have any used sizing screens for producing 1.5 inch gravel. Mine cost me nothing. Measure the length and the width of the fire box brick to brick. You can use a thin disk on a grinder, or oxy-acetylene to cut a section out of the screen to your measurements. I reduced my measurements by 1/4'' to allow for expansion of the grate, and irregularities in dimensions that you will almost always find in older furnaces due to warping of the firebox. All you have to do now is insert the dowel into the anchors and lay the piece of screen on top of the remaining grates and the support dowel. My conversion may not work well for you if you are still burning coal as the finer coal will probably just end up in your ash pan. I changed to wood only and it works fine.