Where can I find frame blocks to roll out a dent in a 531 down tube? I found a source on the web called Paragon Machine Works, but wanted to see if there's a recommended source.

Thanks

I have Paragon Machine Works blocks. Very nice quality.
Some people make their own out of a block of hardwood, using a hole saw of the correct diameter for the bore and a thin kerf saw (bandsaw) to split the block.
Brent

How does that work?

I'd use wood if I had to, but

a) wood is softer and weaker than aluminium - I'd expect that the bearing surface would get marked/damaged/distorted easily; would have to make (an)other pair(s) of blocks;

b) lubing/friction will be less consistent with wood than aluminium;

c) hole saws do not cut accurate or smooth holes (not even Forstner bits). They are meant for making holes that you put something like electrical wiring or heating pipes through - clearance is the goal, and 1/8 inch bigger than nominal size is no problem; and

d) if you don't get the saw split at exactly 1/2 you will have problems getting one of the block pairs around the tube; better to get two blocks with flat faces and bolt them together before making your hole - the centre-line will help keep the drillbit in the middle. (If you are boring the hole this should not be a problem, but drillbits sometimes go where they want to, not where you want them to.)

Thanks!

Sounds like you have not used wood blocks, so I thought I'd respond with my own experience.

I've made blocks out of dogwood, a hard resilient woods that worked well for rolling with none of the damage you mention. If I were to make another set, I'd use Lignum Vitae, which I didn't have on hand at the time. LV is twice as hard and used for shaft bearings on ships.

Why would this be?

I used a forstner bit in a drill press. Accuracy is a function of your equipment, not the material.

I agree that it better to clamp 2 halves and drill down the center (and you really have to use a drill press with the blocks held firmly). A thin saw kerf shouldn't be a significant issue with careful clamping on the frame tubes since it's the nominal radius of the hole that matters.

Wood and metal hardnesses are tested differently, so comparisons are not simple or easy, but back-of-the-envelope-type artithmetic says that 606T6 is roughly an order of magnitude harder than the hardest wood known. Friction and lubrication may be inconsistent because of grain and pores. And the problem of the saw kerf is that if you go off the centre-line either way you can't get one of the halves around the tube.

I argree (partly) about equipment, but drills and drill presses are for holes, not bores - cheap drill-press runout can easily be .1mm. Sometimes accuracy is the result of luck.

Maybe I should try a wood block first to limit some of the damage from rolling out the dent. I have some Ash and Hard Maple on hand-- and a 1 1/8 forstner bit and drill press. Dogwood is much harder than either one though. 2150 vs. 1320/1450 on Janka Scale.

Here's the source (Paragon) for aluminum frame blocks:
https://www.paragonmachineworks.com/.../?q=tube+block
Here's some other relevant discussion:
Top tube dent repairable? esp. Doug Fattic's post #19
Making frame blocks

Here is a picture of a few of my frame blocks. Wood blocks are the foundation tool for any frame builder. They have the right amount of ability to both hold and move the frame without readjusting the vise pressure. Aluminum blocks don't work as well when constantly changing the frame's position. The block on the left is made out of hard maple (that works perfectly for frame blocks and better than most other woods). The one 2nd to the left is made by Paragon Machine Works. The one 2nd from the right was made by Bicycle Research. The one on the right is made out of oak. It works well but doesn't stand up to hard use like a maple one. Its edges chip and its open pores fill with flux.

I buy hard maple just down the road from me from at Johnson's Workbench. They sell online too. I buy it 5/4th thick (I think that is what woodworkers call it). This means it is 5 X 1/4" or 1 1/4" thick. I cut the stock so it is 3" square. I place them together with a piece of cardboard in-between. That makes it easy to know where to center the drill bit. It is important to drill the hole 90º to the grain of the wood or it might eventually break. I have a vertical milling machine and after using a large drill but to clean out the center, I finish the hole with an end mill of the chosen size. A hole saw will work (I've tried them) but they leave a rougher surface and leave a slightly large hole. A piece of leather can make the hinge. I use belts I get at Goodwill if I can't find any leather.

If I am trying to get out a dent, I start with the wood blocks before finishing with an aluminum block.

As Brent has mentioned you can make your own...my only addition/sugestion that I would be to use a Forstner bit, if used slowly I have found the cuts much cleaner and less likely to have rough edges in the bore .
Cabinet and furniture makers use these.
Best, Ben