In reviewing this thread for ideas it occurs to me that there are really two distinct design philosophies for skid plates. One, as represented by Ranch and Wallace is made for full bore, go anywhere without looking, commercial type tractor use. The other, like Bob's, is more limited and really designed more for adding a level of protection against unseen branches and small stumps that might snag the relatively delicate items hanging off the bottom of the tractor such as filters, linkages, hydraulic and electrical lines and connectors and other family jewels. The first commercial type looks like it would be effective against an IED so it enables the tractor to bull its way into brush without loss of time navigating around obstacles. The more limited version functions more like an athletic cup, just protect the delicate dangling bits from unintended contact. I'm thinking more along the lines of building my tractor a jock strap with cup. I'll try to steer away from obstacles (never probe for enemy with your cojones!) and will work around them if I can see them but want protection from that unexpected snap back of a branch or small stump.
The other issue I am pondering is how to attach the plates and whether to build in filter access holes (as Bob did) or just plan to remove the plate for filter changes (once every couple hundred hours for HST is not such a burden and I don't think a plate is needed to protect the area near the oil filter (but that is from memory only)). Attachment via drilling through the "frame" under the operator station is clearly the simpliest way to go. The alternative might be to weld either studs or the mounting brackets to the frame and then use bolts/nuts to attach the plates. Living in areas with salted roads I worry a bit about drilling holes in frames but realistically as my use is on land not highways that is probably unwarranted. It would also greatly complicate installation if one needs to do precision welding under the tractor to weld either studs or angle iron to the frame. The more I think about it the more I believe Bob's approach is the efficient and reasonable way to go.
Another consideration, perhaps a bit over reaching, is whether to use the skid plates as extra low ballast and therefore use heavier steel rather than minimal gauge. Probably not practical but it does seem a good place to have some extra weight.
In looking at Bob's plates more carefully I see that there really are no difficult bends and that there are some angled cuts that would be easier with plasma or torch than with a steel saw or grinder. It also seems that he has used 3/16" steel which should not be hard to bend with a press but which would certainly be strong enough to protect and deflect wayward branches and cut sapling stumps. I had been thinking of 0.125 or even just 12 gauge to protect the area on the left side where the electrical connectors are vulnerable to being snagged. I suspect 12g would be adequate for the hydraulic connectors too but the filter area may deserve heavier sheet. I guess it really boils down to whether I am trying to deflect bendy objects or stop a rigid object like a bigger stump. I'm leaning towards the former as those are the things you often don't see when working in brush and those are the things that are not caught by the
grapple or bucket because they yield and are bend down while you pass over them. In my four seasons of ownership I have disconnected the electrical fittings twice and knocked the hydraulic connectors for the FEL off once. My HST filter is, thankfully, still unbruised. I'm leaning towards lighter duty right now but maybe 0.125 is a reasonable compromise along with some stout angle iron through bolted to the frame. I'm also leaning towards just unbolting the guard when doing filter changes.
I look forward to hearing more from Bob when he returns to see how he would do it the next time.
