How precise is a shaper?

[Conrad Hoffman]

I doubt I'll ever have or have access to a shaper, but I was doing something recently that just screamed out for one. I needed to put a very small V-groove on the surface of a part. It needed a sharp bottom. I ground a tool and fastened it in the mill spindle, then drove the part underneath the stationary tool, about a thou at a time. Worked OK. So my question is how precise is a small shaper? Can it down-feed 0.001" or less? Is it what you'd use for this sort of thing? No doubt I could find some milling cutter to do it, but probably not with a really sharp point like I could grind. Plus, by grinding, I could keep the relief small, which keeps the point strong.

 

[Renardiere]

Conrad, I am sure with a small shaper in good condition you will achieve what you need. I'm in the midst of making a small set of adjustable parallels and have been using a shaper to cut the tiny dovetails with good results.

 

[Mark Rand]

After a decent rebuild and re-scrape, a shaper can be as precise and accurate as any milling machine!

 

[???]

When I did my trade test the tolerance was plus or minus .01mm. I did my test on a Bridgeport but guys a few years older had the choice of mill or shaper and the guys before them only used a shaper. The test pieces included slots and angles. From my experience using them during my first apprenticeship in the army there is usually a lot of packing with cigarette paper etc to get a perfect setup.

 

[Billygoat]

It is only a precise as the operator.

 

[just Dave]

Conrad, I am sure with a small shaper in good condition you will achieve what you need. I'm in the midst of making a small set of adjustable parallels and have been using a shaper to cut the tiny dovetails with good results.

Now that is a labor of love

 

[Renardiere]

Now that is a labor of love

Thanks Dave, I still have a long way to go.

 

[stephen thomas]

Can it down-feed 0.001" or less?

Yes - with a couple caveats.

1.)put an indicator on it.

Either the toolslide is left relatively loose and there is enough mass that it hangs on the lead (downfeed) screw. Lock it securely before commencing the cut.
Or with a snug slide/gibs you have to feed down with the leadscrew...oops!.... and raise back up to take the slop out.
If it is a light cut, that is probably adequate.
If a heavy cut, maybe bring the leadscrew back to bear again, and "estimate" how much pressure to add to keep the toolslide in place.

Cuts on a shaper are subject to the normal way wear any machine is. It was traditional to make cuts for parallel features on work done on a shaper by swapping the work end for end to make both sides of the feature with the same tool set up. This saves time for tool changes (LH to RH, e.g.). But it also avoided the factor that with side pressure, the advancing ram deflects opposite directions if the cut is made first on say the LH side, then the opposite hand tool installed and the RH side cut on the opposite side of the ram. Shapers are/can be quite good for accuracy, but some of the geometry has to be thought through "differently". (FWIW, i probably usually accept the tool change (or use a duplex tool) & do a parallel feature from both sides rather than disturbing a vise set up. The taper is usually quite small if it exists. Certainly on short parts)

Then there is the added factor of the clapper.

Caveat 2.) if the clapper is worn & floating in its box or especially if the pin is loose in any way*, the clapper will rise or diverge in the cut and be un-predictable.

Lifters save wear on the clapper and tool because the tool does not drag on the backstroke, and the clapper does not bounce 7 or a dozen times on the way back either. But they also allow running the clapper more snugly for precise cuts.

smt

*both the taper pin and the hole wear oval, and the hole can go bell mouthed.
So on a worn clapper, it might not be possible to tighten the pin enough to avoid divergence in a cut and still have the clapper function under gravity alone. Besides the fact that the ears of the box probably need reamed to get the pin to actually seat deeper anyway.