[Glidergider]

I'm about to buy some plastic. My MDF adjustment blocks popped a thread yesterday so its time to rebuild in plastic. The plans call for delrin but I've seen several posts to buy HDPE.

On the McMasterCarr.com web page, I was able to determine that Delrin has a tensile strength of 10 ksi while the HDPE is rated at 4 ksi. I don't see any more distingishing atributes for these two product except price.

The Delrin cost $53 while the HDPE costs only $17. I wish I could make this thread into a poll. I'd really like to know what you guys are buying.
thanks,
Dave

[datacop]

HDPE:

Very easy to work with...

Sam's Club cutting board, 15" x 20" x 1/2" for $11.32 (I just bought some tonight)

more than enough to make all the adjuster blocks you'll need.

[Madclicker]

I think HDPE is better for mounting and structural because of price. Acetal (Delrin) and UHMWPE are better for wearing surfaces because they are self-lubricating. Just what I can gather.

[the__extreme]

I'd use the HDPE (or even UHWM http://www.paplastics.com/polyethylene.htm) instead of Derlin (http://www.paplastics.com/acetal.htm). Those are just the links from the local business I deal with. Derlin has slightly lower friction & thermal expansion, and the PE's are more resistant to wear. It goes along with the strength and elastic modulus, but I think Derlin is a little harder than HDPE also. I think you'd be fine with either material, so might as well save yourself some money and go with the cheaper of the two, as others also suggested.

If you're happy with the current MDF blocks, you could always bore out the thread holes a little and insert some T-nuts. They won't strip.

- Shawn

[SCHootie]

I want to make my own acme lead nuts, am I correct choosing delrin for these?

[Madclicker]

I want to make my own acme lead nuts, am I correct choosing delrin for these?

I think so. I used UHMW and am still using them, but I think acetal is the recommended material.

[SCHootie]

Maybe I'll try the UHMW to make sure I can produce a good lead nut, then do them in delrin if the UHMW wears out.

[pinemartin]

Hi All
Want to build a 3 axis milling machine for routering out letters and art work in wood. bewteen 5cm and 8cm deep. can anyone point me in the right direction. been told to check out forums but there are what seem like thousands, hard to know where to start. something rigid and of course user friendly. worked loads in autoCAD, but not with cnc, so easier the better.
Dave. Scotland

[tajord]

Hi All
Want to build a 3 axis milling machine for routering out letters and art work in wood. bewteen 5cm and 8cm deep. can anyone point me in the right direction. been told to check out forums but there are what seem like thousands, hard to know where to start. something rigid and of course user friendly. worked loads in autoCAD, but not with cnc, so easier the better.
Dave. Scotland

You probably can start with downloading the free jgro plans, a good "starter" cnc, you'll find them here, also you can view the threads of those who made this router and see what you think, here the link:
http://www.cnczone.com/forums/forumdisplay.php?f=300

Good luck.

Jordan.

[Glidergider]

The price for UHMW in the 12x12x3/4 size is $15.64. Its tensile strength is 3.2 ksi.

Delrin 10 ksi, $53
HDPE 4 ksi, $17
UHMW 3.2 ksi, $16

It seems the cost is proportional to tensile strength.

Maybe I'll try the UHMW to make sure I can produce a good lead nut, then do them in delrin if the UHMW wears out.

[Glidergider]

I'm curious, how do you know your cutting board is HDPE?
I used a cutting board for my 1/2 inch pipes. Actually mine was slightly less then 1/2 thick. I had to use some washers/spacers under the mounting screws.

I've looked everywhere for a thicker cutting block, but can't find one.

HDPE:

Very easy to work with...

Sam's Club cutting board, 15" x 20" x 1/2" for $11.32 (I just bought some tonight)

more than enough to make all the adjuster blocks you'll need.

[datacop]

If you look at the image.. the first bullet point reads:

Durable: High Density Polyethylene

These aren't quite 1/2" either I measured them last night and they are more along the lines of 7/16".

[Drakkn]

I have just ordered some pieces of nylon block for my anti backlash parts and adjustment blocks - will let you know how it goes

[Glidergider]

Saturday, I went to Sams Club, but they didn't have the Rubbermaid brand cutting board you found. Then I went to Walmart and bought their cutting board. Their label only called it a Poly material. Yesterday I spent way to much time with this material. Cutting it with a scroll saw at medium speed, I found the heat would melt the plastic behind the cut and when cooled, it was almost 80% of the original strength. I dialed down the speed of my scroll saw to its minimum and that helped a lot. Bottom line, all Poly materials are not equal.

Also, this Poly material is brittle. After the inital cutting of the scroll saw, the remelted plastic was so strong, that I struck the seam with a hammer hoping it would break at the cut line. Guess what, the plate broke but not along the cut line.

HDPE:

Very easy to work with...

Sam's Club cutting board, 15" x 20" x 1/2" for $11.32 (I just bought some tonight)

more than enough to make all the adjuster blocks you'll need.

[SCHootie]

I had that same trouble when I was making some parts for my ultralight. I ordered some delrin of ebay and I guess I'll search around for cutting techniques before I make my lead nuts.

[jjones]

Plastic.. Finally something on here I can contribute to!

Delrin (Acetal) is superior in strength and ware resistance over HDPE. Neither are hydroscopic and both are stabil to temp changes. Both should hold threads well and work in most applications, but the Acetel should last much longer.

As far as cutting, I guess it's really down to "speeds and feeds" as they both melt in similar temp ranges. I just cut some large blocks of Acetel on my table saw with pretty good results. It even supprised me!

One added note. Do NOT get acetel to the point of burn. The fumes will cause your eyes to burn and water and it will take your breath completely away. Imagine the strongest onion you've ever smelt and multiply it by 100!

I'm not an engineer, but I've worked in the industry most of my life.

Jim

[vger]

I had that same trouble when I was making some parts for my ultralight. I ordered some delrin of ebay and I guess I'll search around for cutting techniques before I make my lead nuts.

There is a shop here in town called PSF (Plastics Supply and Fabrication) and they have an area where they sell all the drops and scraps. I picked up a piece of delrin 1" X 2" X 13" for $20. Maybe a plastics fab shop in your area ?

I had no problem cutting the delrin on a band saw (metal cutting blade). Also milling it with an end mill was a breeze.

I am using 1/2 10 acme for my little project and made my own acme tap from a short piece of the acme stock. I just chucked a 6" piece up in the drill press and tapered the end with a file. I then milled the flutes with and end mill chucked in the same drill press with a cross slide vise holding the tap. It clogs fairly quickly so I back it out and clear it several times, but it makes a good tight nut!

Steve

[mxtras]

MSC and McMaster-carr both sell most plastics - online pricing, lots of thicknesses available and fast shipping.

http://www.mscdirect.com
http://www.mcmaster.com

HDPE is pretty easy to work with but it will warp with machining and it will 'migrate', or creep under load. Nylon reacts better to machining but will also creep. Delrin is the most dimensionally stable material of the three but the stability comes with a price. All three will likely work for relatively light duty loads. Moisture effects dimensional stability with Nylons and PE materials.

Scott

[SCHootie]

There is a shop here in town called PSF (Plastics Supply and Fabrication) and they have an area where they sell all the drops and scraps. I picked up a piece of delrin 1" X 2" X 13" for $20. Maybe a plastics fab shop in your area ?

I had no problem cutting the delrin on a band saw (metal cutting blade). Also milling it with an end mill was a breeze.

I am using 1/2 10 acme for my little project and made my own acme tap from a short piece of the acme stock. I just chucked a 6" piece up in the drill press and tapered the end with a file. I then milled the flutes with and end mill chucked in the same drill press with a cross slide vise holding the tap. It clogs fairly quickly so I back it out and clear it several times, but it makes a good tight nut! Steve

I actually have ordered some delrin from ebay. It was 10 pieces 13" inches long 1.5" X 1.5". Including shipping it was $30, so I think I got a good deal. As far as the lead nuts, I'm going to try to do exactly what you're doing.

[blasttiod]

HDPE:

Very easy to work with...

Sam's Club cutting board, 15" x 20" x 1/2" for $11.32 (I just bought some tonight)

more than enough to make all the adjuster blocks you'll need.

What cutters are you using ?
I have been trying to cut this stuff but I'm having problems with melting/ cutter clogging etc......

Kevin