Bevel Angle on Four Prong Spur Drive Edges

[Don Stephan]

Often I use a 1" diameter four prong spur drive for "larger" spindle blanks, both green and dry. The blank is stood upright on a 3" thick wood work table directly over a 4" square cross section leg on a solid concrete floor. The edges of the spurs are not damaged. A number of sound blows with a one pound wooden mallet only drives the edges into the end grain at best 1/16" inch. The same result with a brand new 1" diameter four prong spur drive I purchased a year ago. When rounding 3" square cross section spalted beech blanks this week, taking light cuts, several times the drive spun in the end of the blank.

I'm very tempted to try to make a more acute bevel on the spurs with a Dremel or similar tool and bit. Has anyone tried something like this?

 

[hockenbery]

I do all my spindles with a ONEWAY cup drive aka safe center. If I get any spinning just a 1/4 turn on the handwheel corrects it.


I sharpen my spurs on square edge wheel.

Spinning is caused by too little tailstock pressure.
In spindles too much pressure can cause problems.

A band sawn cross an 1/8” deep on the spindle end makes it quick to center the spur and prevents spinnning.
Endgrain can be quite hard. Beech is hard.

I use spur drive to start most bowls and hollow forms between centers.
During turning the centers can work in deeper making a less tailstock pressure. I check tightness in the beginning.
Tatlstocks can move and handwheels can open while turning.
Checking tightness after a few roughing cuts prevents spinning.

 

[William Rogers]

I also use the safe center. I quit using spur drives altogether. One thing I do that help some is I lock the spindle and try and rotate the wood by hand. Tighten the tail stock and repeat. This will seat the drive a little deeper. As Hockenbery said check after a few cuts.

 

[Alan Weinberg]

I also use the safe center.

Good for wood blanks for bowls also? Just ordered one. Thanks.

 

[R Henrickson]

I don't use a spur drive for spindles. Most of the time I use a safe driver/center. Sometimes a Steb. Due mainly to classes with Derek Weidman, I consider slipping a virtue since it mitigates possible catches. I also use a safe driver for most of my multiaxis turning. As suggested above, tailstock pressure may contribute to the slipping. Aggressive cuts may also.

 

[Steve Tiedman]

My new Oneway 1224 came with their safe center. If nothing else it is, uh... showing me that I can get lazy, and/or over-zealous with my cutting practices. In short order it has gotten me to break some bad habits and get back to doing things the right way.

 

[Roger Wiegand]

I don't use one any more, having converted to a cup drive (with the big one from Robust I've driven 20" bowl blanks without a problem), but I'd note that the more acute you make the angle on the spurs the more likely it is that the drive will split the wood when used on spindles.
Tried a steb center for a while and the only thing I fount to be useful for was as a hole saw. The continuous rim of the cup (or "safety") drive actually provides a lot more contact area and a more positive connection. I've only ever experienced slipping on major catches except when keeping the tailstock pressure exceptionally low, as when demonstrating how to cause a catch while using a skew. I really like how the cup center (with the point withdrawn) allows for easy re-positioning of the blank for both optimizing grain pattern on bowl s and for multi-axis work..

 

[hockenbery]

Good for wood blanks for bowls also? Just ordered one. Thanks.

I use a spur drive for bowls and hollowforms.
And spindles that weigh in above 20 pounds or so.

Haven’t tried the big cup from Robust that @Roger Wiegand uses. Looks like a good option

 

[William Rogers]

I have the same one Roger has. I don’t use spur drives, but still use worm screw or faceplate when the situation arrises.

 

[Tom Gall]

Often I use a 1" diameter four prong spur drive for "larger" spindle blanks, both green and dry. The blank is stood upright on a 3" thick wood work table directly over a 4" square cross section leg on a solid concrete floor. The edges of the spurs are not damaged. A number of sound blows with a one pound wooden mallet only drives the edges into the end grain at best 1/16" inch. The same result with a brand new 1" diameter four prong spur drive I purchased a year ago. When rounding 3" square cross section spalted beech blanks this week, taking light cuts, several times the drive spun in the end of the blank.

I'm very tempted to try to make a more acute bevel on the spurs with a Dremel or similar tool and bit. Has anyone tried something like this?

Use a bigger hammer! 😂
Way back when - I used to turn a lot of 2x2 turning squares in exotic woods. Ever try putting a dent in the endgrain of Cocobolo? Most point tools just bounce back at you. This was before safety/cup or Steb centers were available. I resorted to this tactic:

- Mark the center(s) ... and the two sides that are closest to 90º (a lot of my blanks more like parallelograms).
- Stand behind the bandsaw (so you can see you marks) - place one of the 90º sides flat on the table - pull the blank toward you to make a kerf (1/8" +/- ) - repeat on the second flat.
- Put your spur drive point in the center and spurs in the kerfs ... problem solved!

I agree with the others about the safety/cup centers ... this is just another option.

 

[JeffSmith]

I guess I’m odd man out - while I’ll try the large cup drive when I get a chance, more often than not I’ll be using a spur drive for spindles (typically four prong) and for initial centering of bowl blanks - even large ones (usually two pronged). They both get driven in with a mallet, but typically 1/16 - 1/8 is all that’s required. 1/8” for wet bowl blanks is sufficient to get round initialized and a tenon cut. I seldom see spinning on even 20” bowl blanks, but perhaps I’m just a gentler soul when it comes to initial roughing.

As Al mentioned, it’s wise to check the tailstock and tighten as you go, but I seldom have problems with a four prong spinning on spindle stock no matter the diameter. Sharp tools and an easy hand - no reason to hurry an enjoyable process.

 

[Dave Landers]

For spindles, I normally prefer what Craft Supplies calls their safety center (looks like a steb center). I find that, if it spins, I can usually get it engaged again by tightening the tailstock. My experience with 4-prong centers is when they spin, they turn into a drill and don't like to re-engage. My experience - may not match anyone else's.

For larger things - bowls and hollow forms - I always start out between centers. For that, I prefer an Elio drive. Great grip and easily adjustable for grabbing uneven surfaces.

 

[Don Stephan]

Sorry, can't imagine how a safe drive center or StebCenter drive center would be less likely to spin than a four prong drive center.

 

[William Rogers]

@Don Stephan In my experience it is not the “spinning”. Again in my experience if a 4 prong drive spins, it tears up the the wood and impossible to get it reseated accurately. With the safety drive you just tighten the tailstock and maintain the same position. I have had 4 prong drives make a mess if there is even a slight catch.

 

[Steve Tiedman]

@Don Stephan In my experience it is not the “spinning”. Again in my experience if a 4 prong drive spins, it tears up the the wood and impossible to get it reseated accurately. With the safety drive you just tighten the tailstock and maintain the same position. I have had 4 prong drives make a mess if there is even a slight catch.

Generally, I agree, but I keep using them (4-prong). I also have an old dead cup center (tailstock center pre-live tailstock center) that I ground 4 shallow divits into that give the dead cup a little more bite without the spin damage of a 2 or 4 spur. I learned this one from some pro 20 years ago. Ground divits or not, web search dead cup centers, you can probably find them new or used for cheap, and they make respecable drive centers as long as the center pin is still in it. As I've mentioned, it's just been in recent days that I've been using the Oneway safety center that came with my new lathe. They all work, you just have to accept their unique quirks and try to refine your cutting technique.

As for the OP question of bevel angle on the spurs, I have no idea. Probably doesn't matter too much. 15-20 degrees or so? Maybe a bit more?

 

[Tim Hunter]

When I drive a spur center into a workpiece, I often begin with an initial hit or two with the spur center perpendicular to the piece, then tip it over slightly toward each spur for a few hits to concentrate the impact on each spur individually which deepens the purchase of each spur, then finally finish with a few more hits with the spur center perpendicular again. This process will yield a deeper impression of the spurs. I also have a notch ground in one spur for positive rotational positioning when mounting the workpiece.

Tim