Taper Attachment for import lathe

[n4zou]

After years of putting it off I've started building a taper attachment for my 12"X36" import lathe. I'm using this one as a guide. http://www.homemodelenginemachinist.com/index.php?topic=7086.0

I had a peace of 3/8" X 3" X 18.250" hot rolled plate steel I found in the scrap pile that I cut in half at a hole that someone had drilled a slightly offset hole in. I milled both ends and then cut a 22mm wide slot to match the way bed. Tomorrow I'm going to make the clamps. The "C" clamps in the pictures are just for test fitting.

 

[lathe nut]

would love to have one on my 14X40 HF lathe, going to be watching, interested, thanks, Lathe Nut.

 

[n4zou]

Made 4 3/8" X 3/4" X 3" clamps yesterday. Each have 2 3/8-16 taped holes and 2 are used for each mounting plate. 2 25/64 holes were drilled in each of the mounting plates matching the 3/8-16 holes in the clamps. I made sure the tail stock would clear the mounting plates. I'm happy with the clamps and mounting plates. The sine bar will be made of 3/4" X 36" zinc plated bar stock and will mount underneath the mounting plates. A bronze bushing will be used in the bracket that will slide on the bar. I've have a couple of ideas for the brackets that will mount the bar to the mounting plates. this will mostly be determined by what I can find in the scrap pile.

 

[n4zou]

I finished the sine bar and slotted the support brackets for it. I mounted it to the lathe an put an indicator on it. I set the bar for zero taper with the indicator attached to the carriage and found I have .002 run out in 30" of carriage travel. I'm happy with that! I then pulled really hard on the bar and found I could get it to deflect .010. I thought it would be more without any additional support. I was going use a single 1" wide bronze follower bushing that would attach to the cross slide but I think I'm going to use 2 bushings and make it 6" wide. I will not lose any travel making it this wide and it should greatly reduce the deflection. I need to remove the cross slide to drill and tap an additional hole for the cross slide bracket. This project is turning out better than I expected. Pictures below. One shows the sine bar at zero and the second shows the bar set at 6" in 36" which is the maximum taper setting possible. I can't imagine I would ever need to turn a taper that steep. The compound would be a better choice for cutting that taper. The slots in the mounting brackets allow the sine bar to be easily moved without binding. A 1" slot parallel to the bed way at the pivot point allows it to move freely as the other end of the sine bar is moved in it's 6" slot. No way could I ever cut the slot with the required radius of a 36" bar! There's no reason to cut one anyway. Having the pivot move parallel with the bed ways will not effect the setting of the sine bar at all. See pictures of that below.

 

[n4zou]

Did some more work on it today. I made the sine bar follower from a 8" X 3/4" pipe nipple, 2 3/4" to 1/2" pipe reducers, and 2 3/4" X 15/16" X 7/8" bronze bushings. I put the 3/4" pipe in my 4-jaw chuck and using a dial indicator set it dead on concentric. This part must be machined very precisely or the bushings will not line up properly. I then spun on a 3/4" to 1/2" reducer and tightened it up with a pipe wrench. I then bored it out to exactly 15/16". The pipe threads within were completely removed leaving a nice surface for the press fit bushing. I faced off the reducer for the shoulder on the bushing. Using a rubber mallet I "pressed" the bushing into the pipe reducer. I then removed the pipe from the chuck and turned it around and did the same operation to the other end. I removed and test fit the follower on the sine bar. It slid on the sine bar without binding for the entire length of the bar. I then tried putting a little oil on it thinking it would slide even better. The fit is so close it actually binds up with oil. After cleaning off the oil it started sliding easily again. I then started making the bracket that will connect the cross slide to the sine bar follower. I used a 5/8" X 1" X 8" aluminium bar stock that will clamp to the cross slide. I could not bring myself to drill holes in the cross slide. The cross slide overhangs 1" so it will not limit cross slide travel when installed. I milled 1/8" slots in it so it shoulders up on the sides of the cross slide so it can't twist on the cross slide. The bracket that will attach to the sine bar follower is attached with 4 1/4-20 bolts and a 3/16" key so it can't twist as well. C-clamps shown in the picture below are temporary and just for test fitting the assembly.

 

[petertha]

Thats coming along nice! What exactly is involved in 'detaching' the cross-slide from the screw on your lathe so it can be slid by the taper attachment once engaged? My 14x40 import lathe looks a lot like yours so I'm anxious to see how this all works out.

 

[n4zou]

That's easy! There are 2 brass ACME lead screw nuts and a wedge between them with a set screw to remove backlash. All I need to do is run the cross slide to the point where the outermost nut is flush with the end of the lead screw. Then just remove the two screws bolting the lead screw nuts to the cross slide and the set screw. This frees the cross slide so it can float with with sine bar follower. I've tried it already and it works fine. While I was working on it today I set the sine bar to the taper used on plumbing pipe fittings which is 3/4" per foot. This equates to 2.25" stack on my sine bar. I've always hated using pipe dies. Very soon I'll be cutting them on my lathe. Those NPT pipe dies are really expensive too.

 

[n4zou]

I just tested my taper attachment and it works very well. I still need to make clamps to replace the C clamps. I could not wait to turn my first test taper after getting the cross slide attached to the sine bar follower. I was also worried about deflection of the sine bar under load but the wide follower bracket took care of it. I used a 3/4 X 3/4 X 1/2 pipe "T" to connect the follower bracket to the cross slide bracket. I bored it out to just slide over the 3/4 pipe nipple. I put a plug in the "T" and then milled it to fit the gap between the two brackets. I drilled and taped that plug for 3/8-16. I then turned a 1/4" boss on the end of a peace of 3/8-16 all thread and drilled a hole in the 8" pipe nipple which locks the pipe "T" to the follower bracket and the cross slide bracket slot. At this point I removed the 2 bolts and a set screw that attach the lead screw nuts to the cross slide. The cross slide was now free to slide with the follower bracket. I had already set the sine bar for 3/4" in 12" taper so I set up the lathe, chucked up a peace of 3/4" cold roll, and started turning it. It cut the taper just as well had I been making a straight cut without it. Tomorrow I'll finish up this project by making clamps for the cross slide and I will buy some paint for the parts. I also need to get a refrigerator magnet to cover the bolt holes where the cross slide attaches to the lead screw nuts. Chips have already fell through to the lead screw.

 

[Holt]

I have been reading your post with great interest, how do you adjust the size of the taper? have you attached the cross slide nut to the taper attachment for easy adjustment? i cant really tell by the pics, very nice setup!

Holt

 

[n4zou]

I need to produce a video of how this works! I'll see if I can do that. Hopefully I'll have some time to finish it up tomorrow and then produce a video and post it to youtube. Taper adjustment is done on the mounting plate currently attached to the bed way at the headstock. When boring a taper the mounting plates will be swapped from there current locations. I used a ruler laying beside the 6" slot to set a rough adjustment. Then I set a dial indicator magnet base on the carriage and the dial indicator point pressing on the tool post so I could accurately measure and set the taper. I moved the carriage 12" while watching the dial indicator. After slight adjustments of the sine bar in it's slot I was able to get it set so the cross slide moved 3/4" when the carriage was moved 12". Note how the compound is set in line with the cross slide. The cross slide lead screw is disconnected from the cross slide so it's now useless. The compound now takes the place of the cross slide. All NPT plumbing pipe threaded tapers are 3/4 per 12". I'll be able to cut threads on that 3/4" taper as well.

 

[petertha]

One thing that may be advantageous about this setup is the longish radius of the taper setting (pipe). I havent quite figured this out 100% in my mind on your existing pivots, but offer the attached sketch as food for thought. If you had 2 posts of known nominal diameter, one positioned as a fixed datum & the other attached on the end of the swing arm, theoretically you could measure between the gap with a simple caliper (OD tangent to tangent) & hit quite precise angles.

This sketch shows an example: 30" long bar, 0.5" posts & 1 deg taper angle yields a corresponding gap measurement of 0.524". I changed the taper to 1.5 deg & the resultant measurement was 0.785". A big lineal change for a small angle step. So with a vernier accurate to a 0.001"... you see what I mean. I guess one could pre-compute a handy reference table of incrementing angle amounts = X.XXX" gap.

It's maybe not as nice visually as the scribed vernier angles on commercial taper attachments, but unless you are setting lots of different angles all the time, maybe better for home shop purposes?

 

[n4zou]

It only took me a couple of minutes to set it up for 3/4 in 12 inches. I calculated the bar needed to be moved 2.25 inches. I simply used a 6" rule laying beside the slot and moved the bar. I then checked it with the dial indicator and found it was only .008 off. I've used factory taper attachments. You still need to double check with a dial indicator anyway. The marks on the factory built taper attachments are for rough setting just like my 6" rule.

 

[Holt]

What i meant is, you can't take it all in one pass, how do you adjust the depth of each pass?
Back in my youth, i worked with a lathe with taper attachment, IIRC the crossslide handle was somehow attached to the taper, making it possible to adjust the depth on each pass. BTW we turned 45 deg. taper on that lathe although everybody claimed 30 deg. was max for a taper attachment ;D

 

[n4zou]

I used the compound. If you look at the picture you'll see the compound is set parallel with the cross slide.

 

[n4zou]

I finished it up today. I'm very happy with how it turned out. I cut NPT pipe threads using it today. I had to turn the compound dial out at the end of the thread. I had to remember where I was on the last cut and then turn in a couple more thousands. I really need to build this Swingup external threading tool. http://madmodder.net/index.php?topic=2323.0 This would make cutting tapered threads much easier! I also made a pointer for rough setting the taper. I purchased a package of peal and stick magnets and stuck a magnet strip beside the pointer. It holds a ruler in place right next to the pointer. This is much easier than trying to engrave marks on the mounting plate and I can calibrate it just by moving the ruler.

 

[Holt]

I used the compound. If you look at the picture you'll see the compound is set parallel with the cross slide.

Oh i missed that, simple and clever that deserve a carma point!

 

[n4zou]

For threading the compound is set at 29 1/2 degrees but you must wind it out at the end of every pass. I tried reversing the spindle thinking their would be enough back lash to allow the tool to pull away from the threads. That did not work at all. As it turns out there is only .002 backlash on the sine bar. The tool would have rubbed possibly breaking the cutting point.

 

[n4zou]

I used my taper attachment for the first time today. I needed to thread the end of a pipe. It worked perfectly. I started by tapering the end and then set the lathe up for threading. 1/2" NPT is 14 TPI so I set it up for that and started threading it. I skipped most of the repetitive thread cutting passes in the video.
Here is the link to the video of the operation.
[ame]http://youtu.be/XKNOl33JQgE[/ame]