- Joined
- Feb 5, 2015
- Messages
- 662
My boring tool holder was a "temporary" aluminum one made over thirty years ago and … well, everyone knows how that goes, LOL, the temporary one remains permanent. So I added making a new tool holder to "the list" … I had spare time one day so I made one (from steel this time) ! This was the sequence of events:
All of the operations can be performed in the lathe with the existing 4-way toolholder except for the slitting which could be done with a hacksaw. Machining the holder in this manner will assure that alignment with the spindle will be good. Note that if your lathe is not equipped with collets, it might be best to use a small four-jaw chuck so that the various cutting tools can be carefully centered coincident with the lathe spindle axis.
After sawing off a 2-1/2 length of steel 1 x 1 stock, I surfaced one side on the horizontal mill - about 1/8 was adequate so that the bar fit the four-way toolpost. After clamping the steel block into the four-way, the next step is to install a center-drill in the headstock and align the cross-slide so that the boring tool hole will be located in the proper position. Now loosen the lock-nuts on the cross-slide gib screws and tighten all of the screws. (This is important because the slide can move under cutting pressure/vibration.)
Center-drill the steel block (feeding the work by hand with the lathe carriage) then install a 1/4 twist drill in the head stock and drill completely through the block. Use the conventional "pecking" technique to clear the chips and brush the drill point with cutting oil every time it is withdrawn from the hole.
Open up the hole with a 7/16 diameter end mill, the longest one available. Use power feed on the carriage, set to a fine feed rate - the end mill will true up the wandering drilled hole because it will behave like a boring tool. Eventually this hole will need to be reamed and it can only be as straight as the pilot hole. If the end mill flutes aren't long enough to plunge through the entire part, no worries, withdraw it often enough to clear the chips. A long, straight path is required for the next drill and then the reamer which needs to faithfully follow the path established by the end mill.
Now drill out the entire part with a 31/64 drill, again using the carriage power feed set to a fine feed rate. Next install a 1/2 diameter chucking reamer in the headstock and set the lathe spindle speed at around 100 RPM. Flood the pilot hole with cutting oil and then feed the carriage by hand into the reamer. Feed the carriage aggressively - fine rates of feed don't produce good results when using a reamer ! (The reamer should pass through the two inch length of the steel workpiece in fifteen seconds or so.)
After the reamer has passed through the work, brush the chips off, lubricate the reamer with cutting oil and quickly withdraw it from the hole, backing off the carriage with the lathe spindle still rotating. Leave the reamer in the lathe for now.
Install a slitting saw in the vertical mill, set the spindle speed appropriately - the RPM should be about 400 divided by the saw diameter. Carefully introduce the saw into the workpiece and then feed at about 1 to 2 IPM while continually brushing the saw blade with cutting oil. (I prefer performing slitting operations by hand so that I can feel any slight resistance that might indicate that the saw is dulling and in danger of breaking.)
(If a mill is not available this can be accomplished by hand with a hacksaw or jewelers saw.)
Remove the work from the milling vise and touch off all sides on the belt sander or by hand. There will be a burr inside the reamed hole from the sawing operation. This can be removed by sliding the work over the reamer (which is still in the lathe spindle) and rotating the work by hand over the reamer. Do NOT power up the lathe, do the operation by hand - it will only take a couple of revolutions to clean up the part.
There's no need to provide clamping screws in the boring holder, like those that were in the old aluminum holder shown below. The half-dog screws in the four-way tool post provide more than enough pressure to secure the boring tool in the holder.
Here it is with a tiny boring bar installed -
All of the operations can be performed in the lathe with the existing 4-way toolholder except for the slitting which could be done with a hacksaw. Machining the holder in this manner will assure that alignment with the spindle will be good. Note that if your lathe is not equipped with collets, it might be best to use a small four-jaw chuck so that the various cutting tools can be carefully centered coincident with the lathe spindle axis.
After sawing off a 2-1/2 length of steel 1 x 1 stock, I surfaced one side on the horizontal mill - about 1/8 was adequate so that the bar fit the four-way toolpost. After clamping the steel block into the four-way, the next step is to install a center-drill in the headstock and align the cross-slide so that the boring tool hole will be located in the proper position. Now loosen the lock-nuts on the cross-slide gib screws and tighten all of the screws. (This is important because the slide can move under cutting pressure/vibration.)
Center-drill the steel block (feeding the work by hand with the lathe carriage) then install a 1/4 twist drill in the head stock and drill completely through the block. Use the conventional "pecking" technique to clear the chips and brush the drill point with cutting oil every time it is withdrawn from the hole.
Open up the hole with a 7/16 diameter end mill, the longest one available. Use power feed on the carriage, set to a fine feed rate - the end mill will true up the wandering drilled hole because it will behave like a boring tool. Eventually this hole will need to be reamed and it can only be as straight as the pilot hole. If the end mill flutes aren't long enough to plunge through the entire part, no worries, withdraw it often enough to clear the chips. A long, straight path is required for the next drill and then the reamer which needs to faithfully follow the path established by the end mill.
Now drill out the entire part with a 31/64 drill, again using the carriage power feed set to a fine feed rate. Next install a 1/2 diameter chucking reamer in the headstock and set the lathe spindle speed at around 100 RPM. Flood the pilot hole with cutting oil and then feed the carriage by hand into the reamer. Feed the carriage aggressively - fine rates of feed don't produce good results when using a reamer ! (The reamer should pass through the two inch length of the steel workpiece in fifteen seconds or so.)
After the reamer has passed through the work, brush the chips off, lubricate the reamer with cutting oil and quickly withdraw it from the hole, backing off the carriage with the lathe spindle still rotating. Leave the reamer in the lathe for now.
Install a slitting saw in the vertical mill, set the spindle speed appropriately - the RPM should be about 400 divided by the saw diameter. Carefully introduce the saw into the workpiece and then feed at about 1 to 2 IPM while continually brushing the saw blade with cutting oil. (I prefer performing slitting operations by hand so that I can feel any slight resistance that might indicate that the saw is dulling and in danger of breaking.)
(If a mill is not available this can be accomplished by hand with a hacksaw or jewelers saw.)
Remove the work from the milling vise and touch off all sides on the belt sander or by hand. There will be a burr inside the reamed hole from the sawing operation. This can be removed by sliding the work over the reamer (which is still in the lathe spindle) and rotating the work by hand over the reamer. Do NOT power up the lathe, do the operation by hand - it will only take a couple of revolutions to clean up the part.
There's no need to provide clamping screws in the boring holder, like those that were in the old aluminum holder shown below. The half-dog screws in the four-way tool post provide more than enough pressure to secure the boring tool in the holder.
Here it is with a tiny boring bar installed -
