Taper attachment

[Larry42]

My first try at using my taper attachment. I managed to get it adjusted very accurately BUT there was a lot of slack in the connection between the taper bar and the cross slide. The result was the taper wouldn't start for the first 1 1/4" of travel (trying to make an MT4 arbor.) After much fooling around I got the taper made and now need to figure out how to eliminate the slack. I can see where it is, its just going to take a lot of fooling around to get it apart and make a new follower. Discouraging.
There is another issue I have to work out. The DRO doesn't show the actual movements. It came pre-installed but I'm guessing they made no effort at calibrating it. I'm going to use the dials as the references for calibration. They are pretty close to the caliper measurements I get. Will just do many iterations until my caliper readings match the DRO. I need to do the same on my mill DRO. I can see a lot of time to get it reasonably close. Is +- .001 unreasonable to expect?

 

[Chipper5783]

Slack between the taper bar and the cross slide? There has to be a little play. The process of using the taper attachment means that the machine operator must understand that there will be backlash and that they need to manage that back lash (not really any different than any conventional lathe or mill). There should be an adjustable gib (I have a TTA on both my lathes - they are two quite different designs, both have a gib arrangement).

DRO calibration? Mine was good right out of the box. All DROs have an accuracy and a precision specification - as you pay more, these values will get better. However +/- 0.001" (which is up to 0.002" out of whack) is pretty easy. Even a very cheap DRO ought to be better than that.

 

[dlane]

What kind of lathes , Larry, David

 

[bfd]

yes even on the best lathes I have run you always have to go past the start and feed from there to get the slop out bill

 

[jcp]

I've run several different makes of lathes over the years, some new, some well used and a 1 1/4 of slack doesn't sound out of the ordinary for the taper attachment. The machines with telescoping lead screws seem to have more than the ones with detachable screws. Also, the steeper the taper, the less the slack will seem.

 

[Larry42]

The slack isn't in the gibs, they are snug. The slack is in the way the saddle that tracks the taper bar is attached to the cross slide. The real problem comes when not all the slack is taken up at once (at the beginning of the travel) but rather as the travel moves down the bar. There is enough drag in the connection that it isn't just a free moving slack. PM1440HD Taper attachment came already installed on the machine from the dealer.
A MT has a very shallow slope so it is understandable how there would be considerable movement to take up a small amount of free play.
The DRO on the lathe was installed by the dealer.

I bought and installed the same brand for my mill. The instructions say you have to calibrate it once on the machine. To do that well you need a very accurate means of measuring each axis of movement over a considerable distance. Using the dials is my only means other than a 6" caliper. I have drilled a series of holes in a bar and then put steel dowel pins in each hole. Then measured the distances between each, with my caliper, and averaged the results over 30" of movement. Compare that to the DRO readings. Adjust the DRO calibration and do it again, & again, &... Always taking care to move in the same direction and approach each point slowly so that slack shouldn't get in.
It is real hard to feel when you have reached the end of the free play and just barely start to move the table. Any movement of the table destroys whatever accuracy you hope to get. The longer the distance you can measure the better your accuracy will be. My mill is a long way from new and has wear near the center that can't be taken out with gib adjustment (if you want to move towards the ends of travel ever!) I'm just trying to get the best out of it I can.

Lets face it, I am not going to buy a high end set of equipment to do hobby work. The only way I can do any work is by using import stuff, mostly from China. I suspect the Chinese are capable of producing very high quality machine tools but that isn't what the importers can sell at cheap prices.

On the lathe I can measure the cross slide movement very accurately by measuring the change in diameter of a work piece. I have a good set of Starrett micrometers. But we are talking a small movement so any errors are more important. Axial movement is a more difficult thing to measure accurately for me. An 18" caliper would be nice, but....

I'm not quite as stupid as some replies seem to infer. I run a shop full of CNC equipment with travels reaching over 13' but not for hobby metal machining. All of those machines have a means of calibration based on summation of multiples. Simple and very accurate. Easy when you can just program the machine to make the test parts and then stack them up for a measurement.

 

[petertha]

I'm just a noob machinsist wishing he had sprung the extra bucks for taper attachment on lathe from the onset because after the fact installment is more involved including the cross feed mechanism, but I digress...

Any chance that the slider bar/mating shoe assembly is dimensionally 'different' at one end relative to the other & passing that on as free play in the table movement? Sorry I don't have a clear picture of cutting forces relative to the slider bar, but maybe as an analogy like as though the gib was looser at one extent of travel than the other vs. constant the whole travel?

 

[Larry42]

Any chance that the slider bar/mating shoe assembly is dimensionally 'different' at one end relative to the other & passing that on as free play in the table movement?
Possibly,
the system of taking up the slack in the gibs is based on opposing tapered gib parts moved by screws from each end so the shoe assembly slack isn't an issue that way.... I checked the bar , it is more accurately ground than I'm capable of measuring. Now that shoe assembly has issues because of the way it is attached to the cross feed. That is where much of the play is. I've snugged the thrust bearings on the crossfeed shaft but there is slack on the end of the shaft casting. The casting has a relatively thin section With a vertical hole for a pin sticking out of the gibbed shoe assembly. The result is the shoe assembly being twisted side ways (top to bottom) on the bar.

I plan to tke it apart and make a new shoe assembly that fits snug so very little twisting can happen. May also make a part to replace the casting.

Those projects have to wait. The drill block on the router had a bearing failure and have that all disassembled now.

 

[jcp]

Larry, is the angle of T/A bar set in the direction that it will pull the cutting tool into work as it moves down the bed?

 

[Larry42]

In this case it was because It had to move towards a shoulder and also so it could move in a direction that would take up the slack before starting the taper.