Delrin bushing machining?

Hi all,

I'm not terribly experienced at machining delrin, but the wife asked me to try to replace some bushings on the salt & pepper mills. ..odd, but a nifty project none-the-less.

I essentially need a ~ 1/2"diameter bushing , ~1/2" long, with 0.040" wall thickness.

Does one turn 1" delrin rod down to 1/2", THEN bore it out? Or, bore it -THEN machine it down to 1/2"?

Is there a rule of thumb on turning thin wall tubes/sleeves?

Sorry about my naivety & thanks in advance! :-)

B
Reply to
bart
Loading thread data ...

Bore first, insert a close fitting mandrel, then turn. DAMHIKT. Bob

Reply to
Bob

Bart

"One" gets a length of =EF=BF=BD delrin rod and makes the bushing from it. The using your cutoff tool cut it off and then makes another and another as needed.

Bob Az

Reply to
Bob AZ

Not great advice.

Delrin is very active, having considerable internal stress. As a result, it will move with each operation. To avoid problems, I recommend one rough turn the OD, drill undersized, leaving 1/32" to be bored, then take alternate cuts internal and external, until size has been achieved. Each cut can be in the neighborhood of .010". Use VERY sharp HSS tooling with considerable positive rake. Hone the tools well.

Do keep in mind that a bushing of this nature will shrink according to the amount of press, so make the bore oversized by the same amount you use for a press fit.

Regular Delrin doesn't make great bushings. Delrin AF is Teflon filled, and is intended for use for running fits. It machines exceedingly well. It's a light chocolate brown in color.

Harold

Reply to
Harold & Susan Vordos

I would bore it first, then mount it on an arbor while turning the OD to size. This gives the ID some support -- much needed at that wall thickness.

It is all about fixturing. If you do the ID first, you support with an arbor. If you turn the OD first, bore a piece of metal (perhaps

1-1/2" to 2" OD) to fit the OD, slit it radially, and use the chuck to compress it onto the workpiece. Probably would help to leave a step at one end to keep it from walking down into the support. You can turn this off (if you don't need it) as the last step, working from the ID out.

It is a good question, and you'll probably get several variants of suggestions so you can pick and choose. (I didn't see any others when I started typing -- but that may simply mean that my newsreader hasn't updated recently enough to pick up any which are out there.

Good Luck, DoN.

Reply to
DoN. Nichols

Beyond what bart wanted/needed, this is fascinating stuff...

Reply to
cavelamb

"Harold & Susan Vordos" wrote in news:CPDYm.3923$ snipped-for-privacy@newsreading01.news.tds.net:

You can anneal it in a regular oven, which will help. I did a quick Google search on "annealing delrin" and came up with:

formatting link
which has a lot of good info.

I think I would machine it roughly to size, anneal it, and then finish. Sharp tooling is essential, as is keeping it from getting too hot.

Doug White

Reply to
Doug White

wingnut had written this in response to

formatting link
: Hello Bart, Machining delrin isn't difficult. As others have said tools must be sharp with lots of clearance. I would start with the ID. If you have compresssed air, that will help to keep things cool.

One of the other posts recommended using delrin AF(delrin, teflon filled). This is a very bad idea for anything that comes in contact with food. I realize that teflon coated items are common in most kitchens, but when the coatings become scratched or abraded those items are suposed to be tossed out. Bushings, by the nature of their service, are subject to scratches/ abraisions. Ingesting even small amounts of teflon can make you sick (with flu like symptoms).

I would stay with FDA compliant delrin. This link will take you to an example.

formatting link
Good Luck,

Wingnut

------------------------------------- bart wrote:

##-----------------------------------------------## Delivered via

formatting link
Forums Web and RSS access to your favorite newsgroup - rec.crafts.metalworking - 190047 messages and counting! ##-----------------------------------------------##

Reply to
wingnut

Don't need to reinvent the wheel, get a couple of these:

formatting link
correct OD and length just enlarge the ID and your good to go

or these:

formatting link
These are metric size needing a little on the OD and ID and with a little left over for the collet to grab.

There is also nylon tubing that is only $1.10 a foot that has an ID only .010 larger than you wanted so if that slop is OK on a pepper mill then all you need do is cut to length.

formatting link
Hope this helps.

Reply to
Roger Shoaf

Starting with a bushing isn't exactly a wise thing to do. The wall thickness will make holding without distorting very difficult. This material machines so well that it's a piece of cake starting with solid, so you have a rigid portion to hold. The multiple steps I proposed may sound troublesome, but it happens really fast with Delrin.

Harold

Reply to
Harold & Susan Vordos

Harold,

Merry Christmas,

While as always I acknowledge your prowess in the machine shop, I point out that I was not taking issue with your suggestion, but rather I was suggesting a practical alternative.

At issue is a bushing used for a salt and pepper mill, that I assume is operated by a little had operated crank at some speed around 50 RPM and very intermittently.

From the OP's description, this is not a part that has any high tolerance requirements.

From my experience working with plastics, I believe I could enlarge a .375" dia. hole to aprox. .420" dia. with out too much grief.

I really like the idea of using the nylon tubing and just whacking off a half inch.

Did you ever get your boiler to work on waste oil?

Reply to
Roger Shoaf

While I agree that it isn't a part for a missile, it can get very annoying trying to hold a thin wall item. It will end up either out of round, or collapsed, depending on the system used for holding. Solid rod prevents the headache, which is the reason I would not start with a bushing. I agree that it can be done, however. Remember, you're dealing with a guy that has little or no experience. Even a seasoned hand would have some trouble re-doing a bushing, achieving the desired results.

Yes, but only with a small percentage of oil. At the price of heating oil these days, it's a worthy venture to pursue. I found that I can blend 10% waste oil with heating oil and achieve very acceptable results. Much more and the flame changes too much. That could probably be addressed with a different nozzle, but I wasn't interested in spending too much time on the thing.

One of the stores in the "big city" sells citronella lamp oil at a close-out price of $1/bottle (two quarts). I buy everything they have to offer when they do, and use it in the boiler. Being a light oil, I found I can blend more waste oil, up to 20%, and get very acceptable performance. Only problem is, they don't usually have more than about 30 gallons, but it's worth the trouble to me, especially when you consider it's cheaper than heating oil.

Thanks for asking.

Harold

Reply to
Harold & Susan Vordos

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.