Providing hobs to gear cutting vendors 2

[geesamand]

We purchase a variety of helical gears in carburized and ground material. Back when we made them ourselves I know we re-used hobs across designs for maximum cost savings. The challenge is that we now go out to a variety of vendors to get these designs manufactured and often in very low quantity. So the hob that gets used is not exactly ideal for the finished ground form.

I wonder if it might be practical for us to buy the hobs and provide them to the vendor. Something similar to the manner in which we own casting patterns and provide them to whichever vendor needs the hob to produce the part. But I know few details of the realities of the hobbing process and need your advice on the idea.

- Do other gear consumers own their hobs and provide them to vendors?
- How quickly do hobs wear out and require sharpening? (*Very* approximate answer expected)
- Are there standards for hob mounting so that most or all of our hobbing vendors could use the same hob?
- Is there a fair way to ensure a vendor does not put undue wear on a hob, and likewise is there a fair way to ensure we send a suitably good quality hob for them to work with?

Thanks,

Dave

 

[BrianE22]

We buy our own hobs and send them to the vendor when they cut our gears. We used to let the vendor hold them but my fear was that they would use them for other jobs or possibly lose them. On the flip side, when we let the vendor hold the hob, they would take care of sharpening (at their cost).

For one gear we run 300 pieces at a time and the vendor sends the parts and hob back with a note saying the hob needs resharpening. For another larger gear done by the same vendor the hob has lasted years (over 1000 parts) without any resharpening.

"Barber Colman" 5/8" shanks are popular for hobs with shanks.

If you use the same vendor just ask them when they finish the job if they want the hob resharpened before the next job. If you want to dig deeper there are published suggestions for how much hob wear is allowable.

I'd recommend making at least two hobs for each gear. I just got a call yesterday from our vendor stating that they broke the hob. Without the spare I'd be down for months.

 

[mfgenggear]

geesamand

There is factors which in my opinion is better to normally let the vendor take care of the tooling. that said there may be cases where you could supply the hob.

are the parts finished hobbed to blue print.
a ground ground part will require a pre-grind hob.
the diameter of the hob to fit the center distance required to clear tooling or machine obstructions, to cut proper depth.
the AGMA quality will dictate the class quality of the hob.
different vendors usually have standard hob arbors/tooling for holding the hobs in their machines.
depending on the parent material,quality, & quantity will dictate the tool material, High Speed Vs Carbide.
so on.

It's best to stick with one or two vendors & let them worry about the tooling.

but if you insist on controlling the hobs, buy it from the reputable gear vendor who are gear cutting the gears for you, because unless you are knowledgeable about gear cutting, you could have expensive set backs.

Mfgenggear

 

[geesamand]

Our gearing in question is hobbed, carburized, and finish ground. We also require full fillet roots. AGMA 10. When our company cut our own gears in the past we worked successfully from a set of company standard hobs.

Some vendors are supplying our gears with fully ground / full fillet roots. Some vendors do the same but don't have the perfect pregrind hob for the situation, and it leaves incomplete grind cleanup at the root. We also prefer but don't yet require ramped hobs to obtain tip chamfering. Chamfering seems to be the most robust protection against handling damage. So these two points seem to support owning our own hobs.

One-two vendors is not an option for us. We as a company have learned the hard way that business conditions can change and we cannot rely on just one or two vendors to provide both our short lead time specials as well as our longer-lead higher volume production needs.

At this point we can add the requirement for full root grinding and tip chamfers, but that will cause unpredictable lead times and costs since our hobbing vendors will no-quote or jack their prices and lead times to cover new tooling. It will be more difficult for new vendors to come on board.

The other option is to re-establish the panel of company standard hobs and do it in a way that tooling and terms are agreeable (least discriminatory) to the vendor pool. That is the core of this thread and I thank you for your input.

 

[MikeHalloran]

>>>When our company cut our own gears in the past we worked successfully from a set of company standard hobs.<<<

Are you still (were you ever?) actually achieving the cost savings that were used to justify outsourcing, given that you aren't getting satisfactory parts, and you aren't getting even unsatisfactory parts when you need them?

Is the cost of your labor, chasing logistics and quality problems, properly reflected in the cost of the outsourced parts?

Or is that just too far above your pay grade?



Mike Halloran
Pembroke Pines, FL, USA

 

[geesamand]

Our company did at one time "make" most every component except for castings and specialty ops like gear grinding. We had gear cutting, a fab shop, machining centers, and an assembly bay. Most of our equipment was secondhand and it wasn't a big deal if most of those machines were not running at any given time.

A day arrived when nearly all of it was in need of replacement. Our secondhand source from the parent company was no longer available and the cost of the new machines was not going to work. So we kept assembly and now buy all parts complete and we do inspection, assembly, and testing on-site. For a time there was putting a target on your chest for even holding the thought of buying equipment for any reason. That season has past, and I see this as a possible opportunity to boost quality, lead time, and maybe even reduce cost. This forum is providing some assistance with that assessment.

David