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Thread hob or hobbing ??? Anyone heard of this?

RABISON

Plastic
Joined
Feb 17, 2006
Location
UK
Hi chaps , can anyone enlighten me as to what a "thread hob" is ? One of our customers asked my boss if we had any thread hobbing tooling for our cnc lathe ,to which he replied no(not having a clue what the bloke was on about...lol).Then my boss quietly comes to me and asks me but i was baffled also,Ive never heard of this term before, /I tried google to no avail.I am thinking its an old school term or something along the lines of a thread mill. Any takers guys !!! thanks
 
Only in higher leads for rapid motion etc. It has the advantage of cutting full ddepth in a single pass. Mostly used for short threads and worms.

What anyone would want to hob a thread on a super versatile will-cut-absoutely-anything-using-a-single-point-tool turning center is beyond me. I think you were asked a trip-up question.

If your turning center is reasonably talented it will cut any lead with any number of starts. You don't need a hob.
 
Nope The question here was specifically "hob" and that's what I limited my response to.

Saying that, you can roll threads on a CNC machine using a common thread rolling head in a turret station.
 
Jackmo,
Gisholt and Landis used to make thread hobbing machines. It's been so long since I've seen one, I don't remember much about them. IIRC, one of them was set up similar to a Barber-Coleman except the hobb axis was about parallel to the screw and you were limited to the length of the part. The other was a "pass through" machine. That's going back too many years for me.
JR
 
I don't know if I would say "any" lead....that depends on the size of machine and work and the lead. We had an absolutely first rate Monarch Metalist and could not turn a 2.5" - 8 thread. These were long shafts and had centers, so limited room between the center and thread start. Using the latest whiz bang coated carbide threading tools the required surface footage was so high, the heavy slides in machine could not accelerate fast enough to be at the proper feed rate that matched the lead. After it is in the cut by 1/4" or so it's fine, everything is synchronized. It's a case where the machine was too heavy for it's own good.
 
Thanks for the quick response guys, the machine we have is a daewoo puma 400L with fanuc 21i-TB controller.The customer actually has the same machine I think .... just overloaded with work and they wanted us to take some on throughout the year.So me's thinking someone's tryin to be a smart ass then hahaha wait till i tell me boss lol. :cool:
 
Thread hobbing is not unusual. It is a normal operation on a CNC machining center. In Texas I have seen Internal threads hobbed in blow-out preventer parts. The cutter has the form of the thread but is a smaller diameter than the hole and is as long as the thread being cut. The tool is advanced to depth and circular interpolated around the circumference while the Z axis feeds in one lead during the 360 degree interpolation. You actually may have to go a few more degrees than 360 for a nice blend at start and finish. The advantage is that you don't have to have a drawer full of different taps. It would require different cutters for different pitches. I suppose if you only had a single point tool it would take several revolutions but I have not seen it done that way.
I am not an expert on this because I was only fixing the machines and was always interested in what was being made but I know the process is not unusual.
Just reread the original post and noticed it is a lathe in question. Warner & Swasey made SC-28 and SC-36 NC lathes with hobs on the turrets several years ago when the oilfield still wanted hobbed threads. They wanted hobbed threads because a lot of the threads cut on lathes by hand had lead or taper problems and also they liked the scalloped finish left on the surface of the threads because it held the thread lubricant when the connection was made up. I would guess that a CNC lathe with live tooling be able to hop a small thread but the spindles on the W/S hobbing lathes ran clear through the hex turrets and had hydraulic motor drives,.
 
Thread hobbing is thread milling. The difference between a thread hob and a thread mill (when i learned about this 30 yrs ago), was that a thread hob has multiple rows of teeth(looks sorta like a tap) while a thread mill has just a single set. So, while the basic process is the same (circular interpolate x and y while feeding z axis at the thread lead), a hob can cut the entire thread in one interpolated revolution while the thread mill needs to repeat the circular interpolation and z feeds to make multiple turns of the thread. Nowadays thread hobs are just called thread mills as far as i can tell.
 
I recently made a few for a couple of screw machine shops. Both shops using 5" Dia. X1" wide with a 1" mounting hole. The first shop wanted to go with hobbing to get a modified acme thread close to a shoulder, in brass, with faster cycle times and longer tooling life. The hob turns at a 1 to 1 ratio, so it's pretty much in and out. And with 100 teeth, the chip load is extremely light.
The second shop wanted to pull the part from their cnc's and move them to the Wickman's to improve their bottom line.That thread was a modified acme triple blunt start (started about 1/8 of an inch into a turned minor dia.) in aluminum using most of the tools width. They were able to drop the cycle time from just under 5 minutes on the cnc to just under 50 seconds complete on the cam machine.
They do leave a series of flats on the threads, determined by the number of teeth. But still a functioning thread.
The brass part was for a faucet mfr, and the aluminum part was a captive aerospace electrical fitting mfr.
So hobs are still used but both customers said the only other shop they could find to make them was in the UK, at around $1400 ea. I don't know if that was because of the modified thread, but at that price, they're kind of prohibitive for most jobs. Maybe standards are cheaper?
 
I recently made a few for a couple of screw machine shops. Both shops using 5" Dia. X1" wide with a 1" mounting hole. The first shop wanted to go with hobbing to get a modified acme thread close to a shoulder, in brass, with faster cycle times and longer tooling life. The hob turns at a 1 to 1 ratio, so it's pretty much in and out. And with 100 teeth, the chip load is extremely light.
The second shop wanted to pull the part from their cnc's and move them to the Wickman's to improve their bottom line.That thread was a modified acme triple blunt start (started about 1/8 of an inch into a turned minor dia.) in aluminum using most of the tools width. They were able to drop the cycle time from just under 5 minutes on the cnc to just under 50 seconds complete on the cam machine.
They do leave a series of flats on the threads, determined by the number of teeth. But still a functioning thread.
The brass part was for a faucet mfr, and the aluminum part was a captive aerospace electrical fitting mfr.
So hobs are still used but both customers said the only other shop they could find to make them was in the UK, at around $1400 ea. I don't know if that was because of the modified thread, but at that price, they're kind of prohibitive for most jobs. Maybe standards are cheaper?
What would you call these cutters, they cut threads on shafts, full width of cutter sits parallel, one revolution equals a finished thread width of the tool?
Machinery For Sale Photos by dt38k | Photobucket
 
Hi in reference to your Thread Hobs, a customer sent me some drawings, from the 80's, of small thread hobs with shanks on them, and I am making alterations to them. I can not reveal the customer but I am currently recreating the drawings in Solid Works, to aid in the alterations, and will be happy to share them when they are complete.

They also use to make large thread hobs with holes in them, similar to a slab mill, but these would not be able to be used in a CNC machine.
 
I'm pretty sure that they sorted this out to some reasonable conclusion 14 years ago, when the thread was opened. Or, this is a terrible attempt at self promotion...
 
the gear industry it uses hobs to cut worms in CNC Hobbing Equipment, same principal to cut a thread, for example thread grinding a thread,same can be used to cut a worm. single, double and triple start worms.
I have started to see manufacture of new CNC equipment advertising hobs for lathes(live tooling) and mills.
but not for threads , but it can be done. because of the chip load per tooth, and feed rate it does the job well.
is it faster and better? time will tell.
 
Hi chaps , can anyone enlighten me as to what a "thread hob" is ? One of our customers asked my boss if we had any thread hobbing tooling for our cnc lathe ,to which he replied no(not having a clue what the bloke was on about...lol).Then my boss quietly comes to me and asks me but i was baffled also,Ive never heard of this term before, /I tried google to no avail.I am thinking its an old school term or something along the lines of a thread mill. Any takers guys !!! thanks

Wouldn't it have been easier to ask the customer what he meant?

I know this is a very old thread but my question still applies today. If I'm in doubt as to what a customer wants I always ask to clarify. Better safe than sorry.
 
I suppose a thread mill is technically a hobbing tool.
No, not the same, quite a bit of confusion in this thread.

A hob has a thread like a bolt, the form spirals around the tool and has a lead.

A thread mill is a series of teeth that go around the tool straight, no lead.

For thread milling, the cutter moves in to depth, can sit there as long as you want, it's just a series of teeth with no advance, then the machine feeds the cutter a bit past one pitch (if it's a multi-tooth cutter, all the way to the end if it's a single tooth cutter), pulls out, done. Thread mills generally swivel the cutter to the lead angle of the thread, at least for coarse pitches. Thread grinders work the same, there are single-wheel and multi-rib grinders, they either grind the thread in one revolution plus a little, or the wheel has to traverse the entire length of the thread.

Hobbing is different because the cutting area itself moves as it rotates. Imagine a bolt with gashes - that's a hob. Imagine a bolt but the threads are just a series of rings arond the shank - that's a thread mill. Same as in a cnc mill, thread mills have no advance. Imagine what a bitch it would be if they did.
 








 
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