With slow growing cacti, just wondering if you can graft them as seedlings to speed up growth and then un-graft at a later date? I dont like the look of most grafted cacti but dont want to wait years for some species to get to a good size

Hornet,
don't want to put you off, but if you read the 4 sticky posts above yours (this one) it tells you EVERYTHING you want to know. How to graft, why to graft, how to ungraft, what to graft to what.

This question is well and truely covered.

sorry, if that isn't what you wanted.

i read thru them so now know what to do and all that but just want to know if it will work, grafting say a Blossfeldia which are very slow growing as you know, just to get it up to a good size before putting it back on its own roots. Also with Blossfeldia they get to just over 1cm from what i have read so what would you graft seedlings onto?

Most seedlings can be grafted to Pereskiopsis Spathula and yes what you propose can be achieved. What stock you use depends on what plant you plant of grafting and at what stage. I recommend Pereskiopsis, Myrtillocactus and Trichocereus in that order for seedlings but there are many stocks you can use.

Check out the thread I completed in the sticky section "Stocks vs Stocks" and make up your own mind.