Thread tap re-profile?

[Arbalist]

Anyone tried grinding a lead on to a plug tap to make it into a first taper? You've guessed it, I've got a plug tap and need a taper. It's a left hand tap so don't want to buy another! I was going to turn the tap in the lathe then find a way of mounting a Dremel with a stone onto the tool post at a slight angle.

[krv3000]

hi well have you got a bench grinder and a cordles drill thats the way i have din it in the past just put the tap in the drill set the grindre a way then hold the tap in the drill at the angel needed and set the drill a way then tuch on to the grinding wheel  dus that hellp

[Arbalist]

Yes, that sounds good! Will it cut ok once profiled though?

[philf]

Anyone tried grinding a lead on to a plug tap to make it into a first taper? You've guessed it, I've got a plug tap and need a taper. It's a left hand tap so don't want to buy another! I was going to turn the tap in the lathe then find a way of mounting a Dremel with a stone onto the tool post at a slight angle.

Hi Arbalist,

You need to provide some clearance for the tap to cut efficiently. Just spinning it in the lathe with a toolpost grinder won't do that.

I made an attachment some years ago for my T&C grinder which gives the necessary clearance. I could take a few photos and attempt to describe how it works if anyone's interested.

I'm not doing now as it's 4:13 am - I've just got up to get a honey & lemon drink to ease my sore throat which has been keeping me awake and couldn't resist firing up the laptop.

Cheers.

Phil.

[Arbalist]

Thanks for the offer but I don't have a T&C grinder so I would not be able to do it.

[DMIOM]

Anyone tried grinding a lead on to a plug tap to make it into a first taper? You've guessed it, I've got a plug tap and need a taper. It's a left hand tap so don't want to buy another! I was going to turn the tap in the lathe then find a way of mounting a Dremel with a stone onto the tool post at a slight angle.

Hi Arbalist,

You need to provide some clearance for the tap to cut efficiently. Just spinning it in the lathe with a toolpost grinder won't do that. ..... <snip>

Thanks for the offer but I don't have a T&C grinder so I would not be able to do it.

Arbalist,

Before writing the oriiginal idea off, I'd have a close squint from the business end of the tap and see how deep the cutting edge has been gashed into the flutes vs. how much taper you wish to add.

You're probably not going to take a lot off the OD, just enough to get the tap centred and to start the first cuts off at a smaller depth of cut. 

The start of the taper used for location doesn't need any edges as it is in effect just a pilot; its then a case of checking if there's any useable edge left where you're tapering the cutting zone.

If its only for a one-off or a few uses, you may find there's enough edge & relief left to allow it to cut when used kindly (lubricated, backed-off every 1/3 or 1/2 turn, etc.); and maybe withdraw it frequently to ensure the flutes aren't clogged.

Dave

[RussellT]

Depending on precisely what you need it for and how many holes, how deep etc, perhaps you could put the taper in the hole rather than on the tap.

Russell

[Arbalist]

Thanks very much for your thoughts and suggestions guys, very helpful! Yes Russell, tapering the hole is a good idea!

[ImIndoors]

I have done exactly what you wish to do with success.  Nothing complex, I just spun the tap in a cordless drill agin a fine grinding wheel until I had a taper which looked about right, as KRV did.  When I had the thread started I just ground the taper off again to get back my, now a bit shorter, plug tap.

Jim

[Arbalist]

Thanks again guys, I'll be tapping through holes in brass so expect from what you've said it should work fine.

[Meldonmech]

Hi Phil

           Is the tap grinding attachment for your Quorn T&CG ? if so I would be interested in seeing the details

                                                                Cheers David

[mattinker]

Thanks again guys, I'll be tapping through holes in brass so expect from what you've said it should work fine.

I definitely wouldn't modify a plug tap for brass. Do you have a means to hold the tap in line ie. a pillar drill (drill press) mill or is it in a lathe chuck so that you can hold it with the tail stock.

Brass should tap easily, just needs to be kept straight.

Regards, Matthew

[philf]

Hi Phil

           Is the tap grinding attachment for your Quorn T&CG ? if so I would be interested in seeing the details

                                                                Cheers David

Hi David,

I made mine to use on my Union T&C but the principle could be used on the Quorn. My friend who left me the Quorn made one for it but I didn't get that when I inherited it. I'll see if his son can lay his hands on it.

Here are some pics of my attachment.

The main spindle slides on DU bushes in the Aluminium housing. The housing is split with jacking and clamping screws to adjust the fit. The spindle is 25mm silver steel and the end is bored 2MT. I bonded on a piece of steel on to screw cut a Myford thread so it will take Myford collets.

I originally made this for doing the flutes of end or slot mills.

The ring with all the tapped holes is pivoted about two points turned on the ends of the socket screws with lock nuts.

The aluminium block on the spindle has 6 holes - 4 @ 90 degrees and 2 @ 120 degrees so can be used with 2, 3 or 4 flute taps.

The face of the ring is only about 1mm wide and is cut away for 180 degrees.

In use the grinding wheel is set at the correct angle for either a taper, 2nd or plug tap. The angle of the ring has to be adjusted depending on the diameter of the tap and the angle of the taper so needs a bit of experiment. (The idea of all the tapped holes was so that I could use a pointed screw in each of the holes which would locate in a small centre drilled hole so I coul easily repeat settings for different taps - I never got round to drilling all the holes and just use one grub screw to lock it in position.) (In an ideal world the ring would be part of a helix.)

You push the bearings against the ramped ring and rotate it. When the bearing drops off the ramp should correspond with the flute of the tap.









Does this make sense?

A 1" ER Collet extension spindle would fit nicely in the Quorn. (If you can get such a thing.)



Phil.