Determining screw tap size

[Kevin Johnson]

I recently purchased a Woodpecker's QuickLift. The model I purchased, the one with the Rousseau plate, did not come with leveling screws. I need the screws for my homemade table. I contacted Woodpecker's and they agreed to send the screws but I would have to tap the holes. The problem is that I don't know what size tap to use. I was told that the screws are 1/4-28 x 3/8. Can anyone tell me what size tap to purchase? Thanks

[Bruce Page]

Kevin, the tap size would be 1/4-28 UNF which is the fine pitch thread tap.

[Brian Hale]

Use a #3 drill for a 1/4-28 tap (.213" dia.) if the plate is aluminum.

Brian

[Kevin Johnson]

Thanks Bruce and Brian. Bruce, what is does UNF stand for? BTW, Brian, I saw you once at the Timonium woodworking show. It was the day that you were picking up your MM16. I did not who you were when I saw you rolling it out of the building, but you later wrote about picking it up and I saw your picture here on the Creek.

[David Epperson]

, what is does UNF stand for?
Unified National Fine. There are also UNC (Unified National Coarse) and UNEF (Unified National Extra Fine - less common). And NPT (National Pipe Thread).

[Brian Hale]

Small world Kevin! Wish i would have known you at the time, the LOML and i had a heck of a time getting it in the basement and i would have invited you along! LOL (just kidding, of course!) Are you the fellow who was talking to me as i was loading it in my truck?

UNF stand for Unified National Fine. UNC stands for Unified National Course. ANSI classifications.

BTW, i suggest you drill and tap just one hole to start with and see how the screw fits. If it's bit loose, step down to a #4 drill (.209" dia.) for a tight fit, just be careful not to force it too much. Turn it in a bit, back it out some, turn it in further, back it out some, etc.

Brian :)

[John Grossi]

Kevin, make sure you use tapping fluid when tapping the holes Drill the hole, then champher it. Spray some fluid on tap and in the hole. Make sure you keep the tap straight. A few turns one way then back out a turn to clean the chips. Use a new tap and a tap wrench and just go slow and easy. Paul

[Joe Trotter]

Here is a link for tap drill sizes.
I have a large one on my wall from the old days.
Joe

http://www.engineersedge.com/tap_drill_chart.htm