Low Friction Finish

[ptt49er]

I'm currently enrolled in the Mechanical Engineering Tech program at UNC-Charlotte and in my dynamics class we have to build a Rub Goldberg machine. The end result of this machine is to send a wooden block off a ledge to a box located 4 inches from the edge...Kinda like my rough sketch below...

BLOCK________
asdfasdfasdfasd|
asdfasdfasdfasd|
asdfasdfasdfasd|
asdfasdfasdfasd|asdfas | asdfa|
_____________ |______| BOX |

Anyways, to my point...

I need a finish to apply onto the MDF surface the block is going to slide on, that will allow me to use paste wax and reduce the surface friction as low as possible. I was thinking of high gloss poly to a pretty good thickness then a few coats of wax. Anyone have any other ideas?

I'll try to get the actual diagram of what we have to build, and calculate for, in this machine.

Thanks in Advance!!

~Phillip

 

[Travis Porter]

That would probably work, but I would also sand the poly to 1000 or 2000 grit after it has fully cured to really make it slick and smooth before applying the wax.

 

[ptt49er]

i'm debating on finishing the block too...looks like i'll have lots of experimentation ahead of me

 

[DaveO]

I would consider either Shellac or Lacquer because they will be easier to rub out to extremely smooth surface, and faster to apply the needed coats. Poly is very scratch resistant and is hard to rub out well.
Another consideration if the block is small enough is a CA finish. It too rubs out to a very smooth finish, and can be applied quite quickly.
I think that a Carnuba wax coating might be able to be rubbed out smoother than normal paste wax due to it's hardness.
HTH, Dave

 

[Gofor]

Using polishing compound (the white stuff found in any automotive supply store) on the poly will slick it up very well. I use my ROS with the velcro pad and just throw a small piece of terry cloth rag or a piece cut from old sweat pants under it. However, be careful not to make it too slick, especially if you polish the block. The two slick surfaces can bond as tight as glue (high friction because all of both surfaces are in contact), and if there is any moisture could creat a vacuum lock. Light sanding one surface by hand with a fine grit paper in line with how you want the block to move will provide less surface area for friction, allowing it to move easier. Just remember to remove all the sanding grit/dust.
A soft polish like wax may be detrimental if heat and humidity are a factor, as the wax could become "sticky", altho in this case a silicone based auto wax may work well.
Of course you could drill little holes in the base piece and have a bellows blow air up though it to give you an air hocky effect!!

JMTCW

Go

 

[ptt49er]

hhmmm...air hockey effect...hhmm....might have to talk to the group members about that...there is a 10 pt bonus if we do something totally out of the box and I do believe that would qualify, might have to grab a fan out of an old computer and see if that would move enough air, the block is a 1" cube, so it wouldn't take too much...alright, now we're getting off topic...

I applied the poly last night, so this afternoon I'll play around with rubbing the finish out...

Thanks a million guys!

~Phillip

 

[dancam]

Another thought could be to scoop out the bottom of the block to only have side rails that are highly polished. The thought here would be less surface area to contact and also some relief from forming any kind of vacum (slick to slick).

Anyway, just another country heard from.

Good luck.

Dan C.

 

[Gotcha6]

I'd try some ArmorAll on one surface. I think it has a silicone base. A guy in a local VFD used some of that stuff on a bench seat in the fire truck one time & he nearly slid out of the passenger door when he made a hard left turn!! You guys are right about the wax. He should use 2 different finish materials or they could bond together.

 

[ptt49er]

we were given the block, which has to stay as is. I think it's a piece of pine ply.

results from my brief testing...using MDF lifting one end until the block slides down...

the block slide at almost the same point for plain MDF as well as just poly and poly with three coats of wax...so i'm back to square one...

a friend mentioned french polishing...does anyone know where I can find the steps involved in that?

~Phillip

 

[McRabbet]

Here is a primer on French Polishing from Wikipedia.org. There is a "How to..." in this that gives you the traditional step-by-step methodology....

Rob

 

[NCPete]

I got to play with John Lord's Krenov style plane yesterday. 14 coats of shellac on the shoe, and it was slick as gorilla snot!

 

[Gofor]

Try talcum powder.

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