What can I get away with in thousands of an inch in HO?
IIRC, Tony Koester and Andy Sperandio both do this on their hand built turnouts. I would like to do this for a much better look though I am using standard RP25 wheel flanges. (I am not interested in Proto 87 so let’s not go there and yes, I will make sure my wheels are in gauge.) My turnouts are FastTracks ones that someone builds for me with NMRA clearances. I can unsolder and move the points on the ones I have and have him build my new ones at a closer clearance. The turnouts are DCC friendly with powered, gapped frogs, insulated PC ties using a Tortoise to change the polarity.
Theoretically, you can go down as small as 0.040" (minimum flangeway) for the spacing of the open point to stock rail. But your opposite point and adjacent stock rail must be exactly at minimum gauge to prevent picking the open point. Remember that unlike a frog, you have no guard rails. And do you really want such a small switch throw (.040")? I would recommend at least double the dimension at 0.080" or more.
The test that Jack Work and others (including me) used to set the open point distance is to take a truck that you know the wheels are in gauge. Push it in a crabbed position to try and catch the open point. If you can catch the wheel, the distance is too small. If you can’t, you are good to go. If you are right at the edge of catch, add a few thousandths to give yourself a working margin. You don’t want to sacrifice reliability (lack of derailments) for sake of slightly better appearance. As long as you are using NMRA wheelsets, the wheel widths and flangeways are going to be significantly bigger than prototype.
All of this assumes that each point is tied to its adjacent stock rail electrically, and that the 2 points are of opposite polarity to each other. DCC-friendly is a vague term, which tells me nothing. If the points are not of the same polarity as th
Thanks Fred, What I meant by DCC friendly was that with the gapped, powered frog and the way I have the stock rail and points wired I can use a narrower space btw the points and the stock rail and not worry about a short if a wheel touches. Tony Koester answered my question on another site. I wasn’t aware that there are two nibs on the NMRA gauge: the wider “electrical” nib if the frog is not gapped and the turnout wired the way I am going to do it to make it safer, and the narrower “mechnical” nib that is narrower for a safe turnout like mine that will look better. Of course, the narrower space is still wider than the prototype but then again I am using NMRA RP25 wheel flanges. However, in my opinon the improvement is well woth the effort.
As a rule I find that about a 16th of an inch (.0625") is sufficient point clearance for HO gauge and still looks better than what you see on the typical commercial turnout. I sometimes use a scrap of 1/16" stripwood as a spacer when soldering the point to the switch rod, and I always check the clearance with a correctly gauged truck as Fred W. suggests.
While some may disagree, I think the term “DCC friendly” is meaningless. That’s because a turnout built to NMRA standards will work perfectly with DCC whether the points are insulated from each other or not, so long as all metal wheelsets on the layout are correctly gauged. The problems arise from turnouts that don’t conform to standards and wheels out of gauge, especially if the gauge is too narrow. It’s asking for trouble to assume that wheels and turnouts are always manufactured correctly.
Since I build my turnouts with deliberately sub-standard point clearance, primarily for a more realistic appearance, I insulate the points from each other and hard-wire them to the adjacent stock rails.