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Tool hold down bolts
- Thread starter Kazam
- Start date
- Replies 19
- Views 2,313
L Vanice
Diamond
- Joined
- Feb 8, 2006
- Location
- Fort Wayne, IN
Depends upon many things not mentioned in the question. Perhaps rather than bolt you mean set screws (grub screws in UK speak)? It is normal to use flat point or, better, half dog point set screws to clamp tool bits in tool holders because the tapped hole is perpendicular to the tool and you get a large contact area with the tool. Oval point set screws are uncommon, but can be employed against a hardened slanting surface, a condition seldom seen. An oval point set screw will make a dimple in soft metal, not usually a good thing.
Larry
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
Whatever you use, I find it pays to remove the threads on the ends (to just below minor dia) so that they don't flare out and can be removed easily when they break etc etc
L Vanice
Diamond
- Joined
- Feb 8, 2006
- Location
- Fort Wayne, IN
In the USA, we call that a dog point, or the shorter point version a half dog point.
My Swiss Multifix tool holders all have dog point square head set screws to hold the tool bits. I got some used non-Swiss no name versions and found most of the dog points had mushroomed (flared out) from over tightening and some would not back out of their holes. I had to grind the mushroomed portion a little bit while still in the holders to get them out. Then I put them in a lathe and turned the dog point to the original diameter.
Flat point screws have a 45 degree chamfer, but the dog point is better for avoiding mushrooming if the screw is properly hard and not abused.
Larry
thermite
Diamond
- Joined
- Sep 21, 2011
The "physics" of it are not so different from airfield pavement loading.
Point-contact transfers force from one material to the other in a spreading "cone" of force gradually distributed over distance.
The first B-36 to land in England had the original huge, single, nose wheel. It left a crack the length of England's best runway. Aircraft since use rows of wheels in tandem. Look at a Hercules C-130 that can land on dirt.
Toolposts are much the same. Typical 4-Way uses a row of small clamp-screws, not just one large one.
Flat, "adaptable", even "sacrificial", dog points are a Very Good Idea on ALL of those. Some applications, one even uses brass or other softer inserts in the tip.
Hardened round or conical tips, not so good a "general purpose" idea. There must be a good reason, and it has to be planned and done well. See Cazeneuve HBX chuck backplate attach system. Three conical attach screws on radials. I don't LIKE it - but they made it work well and last a long time.
No real gain to create local failure stress in the expensive and harder to replace side of the partners in steel any more than it is with rubber aircraft tires and 12,000 feet of slow and expensive to repair asphalt or concrete.
2CW
TedinNorfolk
Stainless
- Joined
- Oct 17, 2006
- Location
- Norfolk, UK
Use square-headed Unbrako.
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
I thought - ''blimey, that's going back a bit, haven't seen Unbrako squares for eons '' ..they're no longer listed Ted.
http://www.unbrako.com/images/downloads/unbrako_catalog.pdf
billmac
Stainless
- Joined
- Oct 17, 2004
- Location
- Lancashire, UK
thermite
Diamond
- Joined
- Sep 21, 2011
.. and.. they are not YET listing male Torx, either. Didn't think I'd learn to like Torx, but Allen has been a PITA for too long.
"Bristo" anyone?
.. ducks, waddles off, stage left...
Limy Sami
Diamond
- Joined
- Jan 7, 2007
- Location
- Norfolk, UK
Can't say i love mine, but after buying a box of 500 M8 dog point set screws, i can't exactly gather the enthusiasm to make my own. IMHO if your changing things enough thats a pain Sami, you probably would be better served making up more tool holders, that said i currently have north of 20 and could probably use about the same again.
I have come across the screws so mushroomed over, to extract them I
have had to go in with a cut off wheel on the angle grinder. Crank the screws
inwards for clearance. Cut off the offending end, then back them out.
Worse case was a tool holder that was very close to the size of the opening, the mushrooming so bad,
I couldn't even retract the screws enough to release the tool.
have had to go in with a cut off wheel on the angle grinder. Crank the screws
inwards for clearance. Cut off the offending end, then back them out.
Worse case was a tool holder that was very close to the size of the opening, the mushrooming so bad,
I couldn't even retract the screws enough to release the tool.
DMF_TomB
Diamond
- Joined
- Dec 13, 2008
- Location
- Rochester, NY, USA
.
screw rounded on end usually contacts a separate piece of metal with cone shape spot face.
1) loose piece can swivel if angles are not perfect 90 degree to screw
2) if vibration heavy less likely the loose piece moves out from under screw cause captured from spot faced hole to prevent moving
.
have seen 30 hp cnc and loose flat block with no spot face vibrates free from under the pusher screw then part in fixture starts moving from heavy vibration. obviously that can be a bad thing to happen
TedinNorfolk
Stainless
- Joined
- Oct 17, 2006
- Location
- Norfolk, UK
Old stock I come across at vintage shows etc. I believe Crawfords at Frithville,near Boston still has them in stock.
EPAIII
Diamond
- Joined
- Nov 23, 2003
- Location
- Beaumont, TX, USA
When I did my QCTP design and construction I rounded the ends of the SHCS that I used to secure the tool bits. My reasoning was that these screws, as supplied, had rolled threads and that process produced an end that was somewhat irregular with a raised ring and a recessed center. I had had problems with standard SHCS on other tool holders mushrooming to the point where they could not be removed after some time in use. A dog point screw would prevent this, but I was using the standard SHCS. So I did round them so that the distortion would occur in the center only.
I was also thinking that the irregular, raised ring from the thread rolling process might try to move the tool bit as I tightened the screws. I am not sure that the dog point completely avoids this problem as it would have to be completely flat and not tilted at any angle. Things are never perfect.
I was also thinking that the irregular, raised ring from the thread rolling process might try to move the tool bit as I tightened the screws. I am not sure that the dog point completely avoids this problem as it would have to be completely flat and not tilted at any angle. Things are never perfect.
The only reason I would do that is to not mushroom the end of the thread so you can get the bolt out when you need to.
As mentioned above Dog Points are made for this purpose. If you don't have access to Dog Points... then Yes, take the bolts to a pedestal grinder or sander and grind a decent chamfer on the end.
Mark Rand
Diamond
- Joined
- Jul 9, 2007
- Location
- UK Rugby Warwickshire
Along the lines of the square head vs socket head comments, why the bloody hell do tools have Torx and Allen socket screws for the inserts. Grrr.
thermite
Diamond
- Joined
- Sep 21, 2011
What else could they have instead that'd actually be enough better to displace them in the marketplace?
Or even as good?
Mark Rand
Diamond
- Joined
- Jul 9, 2007
- Location
- UK Rugby Warwickshire
T15 male Torx would be a step in the right direction...
thermite
Diamond
- Joined
- Sep 21, 2011
I had a fondness going for Bristo at one time. The crisp precision of it, perhaps.
Torx first arrived? I initially figured it just another slip-and-cuss variation on Philips.
I've learned to respect it. Even like it.
Until something better arrives, anyway. They are ALL compromises for solid metal, after all.
Bit like that time someone asked Steve Ciarcia what his favorite programming language was.
"Solder", he replied.
I chuckled. Not for me. Wire-wrap, rather. Easier to correct f**k-ups ...more than once!
