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TAPPING GUIDES - HOME MADE

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In my lifetime I have broken two taps, both of them were M3.

I finally found some time to make some tapping guides to use in the lathes and milling machine.

The guides keep the tap handles in line with the axis of the hole being tapped. This helps to prevent the tap from bending off the axis, and goes some way to prevent tap breakages.

I made a Spring Loaded Tap Guide and some Tap Guide Sleeves.

The Spring Loaded Tap Guide will work in the lathe and the mill. However, the available space in the hobby sized mills may not be tall enough to accomodate this longer guide.
The Tap Guide Sleeves are intended for the mill, and require a rotating chuck. You will need a rotating chuck, or some kind of adapter, to use the Tap Guide Sleeves in the lathe.

 

↓ 1. Spring Loaded Tap Guide.

 

↓ 2. Tap Guide Sleeves.

 

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[1] SPRING LOADED TAP GUIDE

 

↓ Here are the parts that are very easy to make.

 

↓ The dimensions in mm are:-

Body - length - overall = 120
Body - length - thick end = 44
Body - length - thin end = 76
Body - OD - thick end = 18.3
Body - OD - thin end = 12.3
Body - ID - thick end = 10 reamed
Body - ID - thin end = 10
Body - screw holes - both tapped M5
Body - screw holes - centers - 12 in from end
Body - set screw front = M5
Body - set screw front - overall length = 7.7
Body - set screw rear = M5
Body - set screw rear - overall length = 6.4
Body - set screw rear - head diameter = 5.5

Barrel - length - overall = 52 (from 8+10+24+10)
Barrel - length - pointed end = 8
Barrel - angle - pointed end = 60 degrees
Barrel - length - flat = 24
Barrel - length - either side of flat = 10
Barrel - OD = 10
Barrel - recess - to suit spring

Spring - length - uncompressed = 92
Spring - OD = 9.25
Spring - wire thickness = 0.9

 

↓ Construction notes:-

I made the body from 19mmm OD mild steel round bar.

The bore for the barrel and the smaller OD part of the body that goes in the chuck must be concentric, else the job is not worth doing.
I used a four jaw chuck.
I used a DTI to ensure the round bar was running as true as I could get it. The round bar was not perfectly round, so I compromised.
I turned the smaller OD part of the body first.
I then reversed the workpiece and held it in the four jaw chuck by the smaller OD part.
I used a DTI to ensure the small OD part was running perfectly true (within 0.02mm).
I then drilled out the entire bore to 9.5mm. This allowed the spring to comfortably fit in the bore.
I drilled out the barrel section of the bore to 9.8mm, and finally reamed the barrel section to 10mm.
I finished up by skimming the OD of the barrel section.

The barrel was made from a reclaimed printer rod, which was exactly 10mm OD. This avoided having to turn the OD.
The barrel must be a good fit in the body; not too loose, and not tight.
The barrel is a light sliding fit in the body.
The barrel to body fit must not be too loose.
The barrel to body fit is close enough to compress the air in the barrel.
When the barrel is inserted into the body by 90%, there is virtually no side play.

The rear set screw is optional. I needed it.
Both set screws have a plain turned down portion to avoid damage to their threads.
The front set screw retains the barrel in the body.
The barrel can be pushed fully into the body, and the rear set screw can be screwed in a couple of turns to lock the barrel in place. See text below.

The front set screw was made from an M5 hex stainless set screw.
The rear set screw was made from a brass M5 slotted machine screw.

The spring was found in my box of reclaimed springs.
When the barrel is pushed into the bore, and the spring is compressed by 22mm, the spring exerts a 1kg force on the barrel. I measured this on the kitchen scales, like Mr Pete did.

 

↓ Here is the barrel.

The shallow recess in the rear of the barrel neatly captures the end of the spring.

I did not harden the barrel. If it wears, I will make another one.
I left the flat with a milled finish. Someday, I may have at it with a file to make it look better!

 

↓ The two set screws catch the barrel at either end of the flat portion, and stop the motion of the barrel.

In normal operation, the front set screw is screwed in far enough to catch the barrel. This screw does not need adjusting once it is set.
In normal operation, the rear set screw is loosened and does not catch the barrel.
For storage, the barrel is push fully into the body and the rear set screw is tightened to catch the barrel.
My storage tray is not too long, and the reduction in length allows the guide to fit neatly in the storage tray.

 

 

 

 

↓ Here is the guide in the storage tray, in the unextended state.

 

↓ The barrel travel is 22mm.

Here is the guide in the extended state.
The front set screw is catching the barrel, and is preventing the barrel from coming out any further.
The rear set screw is loose and is not catching the barrel.

 

↓ Here is the guide in the unextended state.
The barrel has been pushed in by hand, the rear set screw has been tightened, and the rear set screw is catching the barrel.

 

↓ Here is the guide in use on the lathe.

The tapping guide tool is pushed against the tap holder, which pushes the barrel back into the body of the tapping guide.
The barrel is under maximum tension from the compressed spring.

 

The tapping is complete and the barrel has moved out of the body during the operation.

 

 

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[2] TAP GUIDE SLEEVES

 

↓ I bought the 'T-Handle Tap Wrench Set of 4 - 1/16 to 1/2 - 060-250-02500' from ArcEuroTrade.

 

I made some tap guide sleeves to fit the 3 smaller sizes in the set.

 

↓ Here is a tap wrench and sleeve.

 

↓ The tap wrenches in the set vary in size, so the dimensions of the 3 sleeves vary in size.

Dimensions in mm of largest sleeve:-

length - overall = 62
length - thick end = 42
length - thin end = 20
length - handle slots = 32
width - handle slots = 7
OD - thick end = 19
OD - thin end = 12
depth - bore = 34
ID - bore = 15.7

Construction Notes:-

I made the sleeves from 19mm round bar.
Remove the tommy bar from the tap wrench. Don't lose the spring and detent pin!
In the lathe, turn the round bar down to create a thin end that is 20mm long and 12 OD.
Reverse the work in the chuck.
Ensure the thin end is running true.
Drill out the majority of the bore to a depth of 34mm.
Bring the bore to its final size using a boring bar. I used a Glanze boring bar, with a CCGT tip.
Carefully creep up on the bore ID, until the end of the tap wrench is a tight fit in the bore. You want a tight fit at this stage.
There were some sizes stamped onto my tap wrenches, and their protusion above the surface affected the fit.
Transfer to the mill.
Mill the slots for the handle. This can be a loose fit, but not too loose please.
Deburr and then test fit the end of the tap wrench in the sleeve. My fit was very tight and I struggled to insert the tap wrench fully into the bore. This is what I was aiming for.
I put the sleeve back in the lathe, applied some valve lapping paste, and lapped the bore and tap wrench until a good running fit was achieved. The raised markings virtually diappeared.
The tap wrench needs to move easily in and out of the bore, but with the minimum amount of side play.

The sleeves are like tuning forks, and they ring for a long time!

 

 

↓ Sleeve on the tap wrench.

 

↓ NB: I did not make the bore deep enough.
The handle is 5mm away from the end of the slot.
Luckily there is enough material to allow me to safely bore out the bottom of the bore, so that the handle can come to rest at the end of the slot.

 

↓ I was impressed with the quality of the ArcEuroTrade set.
The tap wrench handle is retained by two machined grooves, and a detent pin.

 

 

 

↓ Here is a bar being tapped M6.
The chuck, guide sleeve, tap wrench, and vice all eat into the available space.
More space can be gained by using collets instead of a chuck.

 

↓ Here is a bar being tapped M5.
There is a bit more space with this smaller tap wrench.

 

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